Summary Six patients with homograft aortic valves who developed endocarditis due to infection with Candida albicans or C. parapsilosis were found to have serum precipitins and high titres of agglutinins to several species of Candida. In 14 of 62 other patients undergoing open-heart surgery, a similar serological pattern developed in the 2nd wk after operation, suggesting the possibility that otherwise undetected candida infection was present. A further 13 of the 62 patients developed antibodies to a single species of Candida. Such patients, especially those with homograft valve replacements, should clearly be watched carefully for infective complications.