NUMEROUS surveys attest to an increased rate of vaginal candidosis and of carriage of Candida albicans during pregnancy (Stough and Blank, 1958 ; Clarke and Solomons, 1959; Mizuno, 1961). Some 10 per cent. of all patients at Queen Charlotte's Maternity Hospital have clinical evidence of vaginal thrush that can be confirmed by culture of the fungus in the absence of other vaginal pathogens (Hurley and Morris, 1964). Many more have minor degrees of vaginal morbidity that may be causally associated with thrush fungi (Carroll, Stanley and Hurley, 1971 ; de Fonseka, 1972). More serious infections caused by C. albicans and other pathogenic species of Candida occur in obstetric and gynaecological practice, and five fatal cases of systemic candidosis were described by Fox (1971), who reviewed 11 other cases. Symptomless carriage of C. albicans may occur in the vagina, and the fungus cannot be isolated from all clinically typical cases of thrush. A serological test might therefore be of value in the diagnosis of superficial as well as of systemic candidosis. Many serological tests have been devised, including agglutination, complement fixation, and direct and indirect fluorescent antibody staining tests (Winner, 1955; Vogel and Padula, 1958; Kemp and Solotorovsky, 1962; Lehner, 1965, 1966). At present, precipitin tests hold most promise, although until recently a positive result was held to be diagnostic of systemic candidosis, candida granuloma or chronic mucocutaneous candidosis. Doubt is cast on this by the occasional presence of candida precipitins in the sera of healthy persons (Chew and Theus, 1967; Pepys et al., 1968) and by their fairly frequent presence in the sera of patients undergoing cardiac surgery who did not develop systemic candidosis (Murray, Buckley and Turner, 1969). We now describe the distribution of candida precipitins in the sera of 303 pregnant women and comment on the probable significance of their presence. MATERIALS AND METHODS Preparation of antigens Three antigens derived from a strain of Candida albicans, group A (London School of Hygiene and Tropical Medicine no. 3153), were produced in bulk to minimise batch variation and stored in the freeze-dried state. (a) Mickle-disintegrated cytoplasmic antigen. A modification of the methods of Stally- brass (1964) and Taschdjian et al. (1964a) was used. The fungus was grown in shaken culture at 37°C for 48 hr. The culture medium was modified Sabouraud's glucose broth (peptone