The present study consists of five chapters. Chapter 1: Deals in the Epidemiology of Fasciolosis in crossbred cattle. It was undertaken at slaughter houses, livestock farms, veterinary hospitals and in household crossbred cows under different climatic conditions in four districts of Punjab Province. Infection rate 18.75%, 15.17%, 15.67% and 13.50% at slaughter houses, livestock farms, veterinary hospitals and in household crossbred cows was recorded respectively. Overall the highest season wise prevalence was recorded 36.50% during autumn and the lowest was recorded 7.88% during summer season. It was also observed that the highest infection rates were recorded in older crossbred cows (above two years of age) than younger (below two years of age). Sex wise prevalence indicated that males were commonly more affected than females. Prevalence was the highest at Sialkot 17.92% followed by Lahore 17.67%, Attock 17.25% and Multan 10.25%. Chapter 2: Deals in the prevalence and ecology of snails. In the present study seven snail genus belonging to Pulmonata and Prosobranchia classes were collected from four districts (Lahore, Sialkot, Attock and Multan) of Punjab Province. These genus were namely Lymnaea, Indoplanorbis, Bulinus, Physa, Gyraulus, Bellamaya and Oncomelania. District wise prevalence of snails was the highest at Sialkot 16.34% followed by Attock 14.15%, Lahore 11.53% and Multan 9.33%. Season wise prevalence of snails was higher in Summer season and Autumn followed by Spring and lowest during Winter. Factors affecting snails population were also studied under field conditions including temperature humidity, rainfall and pan evaporation. Chapter 3: Deals in the role of meteorological data in the prevalence of parasites and snails. Temperature plays very vital role in the onset of disease. Temperature has affects on the metabolic processes of both, snails host and parasite, thus interfering with parasite reproduction within the snail, snail growth and snail survival rate development of various larval stages of fasciolosis takes place within and outside of snail. At temperature 100C little development of larval stages of parasites takes place. No cercarial transmission occurs at 50C. The ideal temperature range is 22 – 250C where development within the snail takes place in an efficient manner similarly humidity range from 55 – 70% is ideal for the cercariae and snail. Rainfall is very important to complete the life cycle of Fasciolosis and also it helps in the spread of cercariae from one place to other. The role of pan evaporation has also been discussed by various workers. Chapter 4: Deals in the therapeutic trials against Fasciolosis in crossbred cows. For this purpose a total of one hundred and ten crossbred cows were used in eleven controlled experiments to compare the efficacy of certain indigenous herbal drugs, including Nigella sativa seeds, Fumaria parviflora aerial parts, Flemingia macrophylla aerial parts and with one allopathic drug Triclabendazole against Fasciolosis. Efficacy was quantified by determining the difference of eggs count per gram faeces (EPG) on pre and post treatment. Firstly, with Nigella sativa seeds, on 1st dose of 80, 100 and 120 mg/kg body weight at 18th day the EPG reduced to 46.34%, 51.35% and 66.67% respectively and after the 2nd dose at 28th day the respective reduction in EPG was 82.93%, 89.19% and 97.44%. Secondly, with Fumaria parviflora on 1st dose of 80, 100 and 120 mg/kg body weight at 18th day the EPG reduced to 53.66%, 56.10% and 50% respectively and after the 2nd dose at 28th day the respective reduction in EPG was 85.37%, 90.24% and 90.48%. Thirdly, with Flemingia macrophylla on 1st dose of 80, 100 and 120 mg/kg body weight at 18th day the EPG reduced to 64.10%, 73.17% and 74.36% respectively and the after the 2nd dose at 28th day the respective reduction in EPG was 87.18%, 92.68% and 94.87%. Fourthly, with Triclabendazole suspension on 1st dose of 10 mg/kg body weight at 18th day the EPG reduced to 67.50% and on 2nd dose at 28th day the EPG reduced up to 97.50%. Chapter 5: These herbal drugs played a vital role on various blood parameters when treatment was rendered to infected animals. During infection serum enzymes were recorded as SGOT (85.37u/L), SGPT (45.40u/L) and LDH (4157.83u/L) which were decreased to approximately normal values after treatment as SGOT (78.50u/L), SGPT (43.97u/L) and LDH (4042.47u/L) respectively. Whereas, some increase in serum electrolyte of infected animals was observed i.e. sodium (140 mmol/L) and magnesium (0.16 mmol/L) but a little increase in calcium (0.56 mmol/L) and potassium (5.82 mmol/L). When infected animals were treated with these herbal and allopathic drugs it played a vital role on various blood parameters and reduced the elevated values of serum electrolytes as sodium (134.43 mmol/L), magnesium (0.15 mmol/L), calcium (0.54 mmol/L) and potassium (5.07 mmol/L). Chapter 6: References.