The combined use of complement fixation (CF) and latex agglutination (LA) tests is reported on sera from 6328 patients with suspected hydatid disease; 191 were confirmed positive at operation (‘known positives’). Results by LA are related to CF titres.

Both tests were negative in 90% of specimens. Nine patients were subsequently found infected of whom 3 became positive in tests after operation.

Of sera positive in both tests, 75% were from ‘known positives’. The remainder were almost certainly from infected patients.

Half the patients whose sera were La positive/CF⋜¼ were follow-up ‘known positives’ in whom CF titres had waned; 2 were early infections.

Only 3% of the cases with an LA negative/CF titre of ⋝1/16 were ‘known positives’ and 6% where the CF titre was 1/8. The remaining CF results in the group were false positives and accounted for 1.2% of all sera tested. Findings show that a CF titre ⋝1/8 with positive LA indicates past or present infection; a negative CF test with positive LA usually indicates past infection; rarely, infection is present when a CF titre is ⋝1/8 and LA is negative. A rising CF titre and positive LA indicates current infection; reliable prognosis following treatment is given by CF.