Four paediatrics patients affected by Chronic Mucocutaneous Candidiasis associated with hypoparathyroidism have been studied. In vivo and in vitro responses to Candida albicans antigens and to other common antigens (Dermatophytin T, Varidase), the percentage of T and B cells and the response to the selective polyclonal phytomitogens (PHA, ConA, PWM) have been investigated in order to quantitate and functionally characterize the B and T lymphocyte classes. The HLA A an B typing has been also performed. Our results show a remarkable and most likely primitive impairment of the T cells, unresponsive either to the C. albicans and the two other skin test antigens or to the selective polyclonal mitogens in vitro. The infectious disease (Mucocandidiasis) is most likely secondary to the T-cell failure. The association between the Mucocandidiasis, hypoparathyroidism and the T-cell deficiency is probably due to a common primitive disembryogenetic defect.