Abomasa were collected from 183 dairy and 186 beef cows in south-west Scotland and examined for the presence of nematodes. One hundred and fifty-two of the dairy cows (83 per cent) and 154 of the beef cows (83 per cent) had Ostertagia species worm burdens of less than 1000; 4 per cent of both dairy and beef animals had more than 10,000 ostertagia present. The only other nematode detected was Trichostrongylus axei and this was present in low numbers in 23 cows (13 dairy and 10 beef). A marked seasonal fluctuation was observed in the proportion of adult and fourth larval stages of ostertagia present. Over 70 per cent of the burdens from October through to April were fourth larval stages. In contrast less than 20 per cent of the burdens from May to September were fourth stage larvae.