By means of crossed immunoelectrophoresis with intermediate gel the precipitins to C. albicans in sera from 18 patients with deep Candida infection were compared with the findings in a control material consisting of sera from 169 'normal' controls (mainly healthy blood donors), 25 patients with oral candidiasis, 14 patients with vaginal candidiasis, and 6 persons without candidiasis giving false positive reactions by the double diffusion method. Up to 20 different precipitins were found in individual sera, and precipitins were demonstrated in all sera except in 6 'normal' controls. Of 692 precipitins 682 (98%) were identified and titrated in terms of the 78-component reference system described earlier for C. albicans. No free Candida antigens were found, but would have been detected by the method. The best criterion for discrimination between sera from patients and controls was the precipitin score, which accounts for number of precipitins and for titres. A precipitin score of more than 6 1/2 had a diagnostic sensitivity of 88.9% and a specificity of 99.5%. Eleven precipitin specificities were found solely in the patients' sera, but the highest sensitivity for a single precipitin was 33%. Until more evidence has accumulated in favour of a monospecific immunoassay it is therefore rational to use a complex antigen extract for further evaluations of diagnostic Candida serology and a short cut to standardization would be the introduction of the method used in the present study.