Humoral and cellular immunologic parameters were evaluated in 13 prepuberal cryptorchid boys before, during and 3 months after hCG therapy. Before treatment, all the immunologic parameters were normal except for a higher percentage of T suppressor-cytotoxic cells (CD8+). During therapy, the percentage of CD8+ cells and lymphocyte response to ConA significantly decreased, and returned to the control level after hCG withdrawal. The possible effects of long-term hCG treatment on the immune system remains to be determined.