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Haemonchus contortus was the predominant parasite of sheep at an organised farm in the semi-arid zone of Rajasthan (India). The worm-egg counts in adult sheep rose to a peak in August while, in young sheep, a peak was observed in September. There was only marginal fluctuation in egg count of advanced pregnant/lactating ewes up to nine weeks post-lambing indicating absence of typical peri-parturient rise in Malpura (native) breed. Coprocultural study indicated the presence of H, contortus and Strongyloides papillosus throughout the year, Trichostrongylus spp. during pre-monsoon and Oesophagostomum columbianum during summer and monsoon. The abomasal worm count showed predominance of H. contortus and maximum worm count was recorded in August. With the onset of winter, higher numbers of immature H. contortus were recorded. Young sheep harboured more worms than did adults. Herbage larval count showed availability of larvae on pasture during monsoon. It was concluded that the period from July to October seems to be more favourable for H. contortus in this agroclimatic zone. (C) 1997 Elsevier Science B.V.