Precipitins to mannan and cytoplasmic antigens of three Candida species were determined in an unselected series of 289 non-pregnant women. Precipitins were present in 20% of sera of women with vaginal candidiasis, in 23% of women harbouring yeasts in the vagina without clinical signs of infection, and in 21% of women harbouring yeasts in sites other than the vagina. Of the 47 patients who reacted with Candida albicans mannan or cytoplasmic antigens, 98% reacted with mannan antigen but only 13% with cytoplasmic antigen. The inclusion of mannan and cytoplasmic antigens of C. guilliermondii and C. parapsilosis did not increase the specificity or sensitivity of the test in the diagnosis of vaginal candidiasis. It is suggested that the double diffusion test is of doubtful value as an adjunct to the diagnosis of vaginal candidiasis.