The rare disorder of chronic mucocutaneous candidiasis is described in a two-year-old African girl who had a moderate lymphopenia due to fewer T and B cells, impaired lymphocyte transformation to PHA and candida antigen, decreased leucocyte migration inhibition to candida antigen and a defective cutaneous delayed hypersensitivity reaction to candida antigen and dinitrochlorobenzene. The patient's serum had a marginal inhibitory effect on the transformation of normal lymphocytes to candida antigen and no effect on PHA stimulation of these cells, as measured by stimulation index. In addition, IgA was deficient in her serum. No associated endocrinopathy was detected and she had a mild iron deficiency anaemia. There was a rapid and excellent response to ketoconazole with all lesions clearing within two months of treatment.