Cell-mediated immunity (CMI) was evaluated in five patients with cutaneous sporotrichosis and six patients with systemic sporotrichosis. Whereas patients with cutaneous disease showed normal CMI, the patients with systemic disease had significant abnormalities in CMI. Most patients exhibited responses to a sporothrix antigen, measured either in conventional assays of lymphocyte transformation or in preincubation assays. Two patients with protracted illnesses and continued abnormalities in CMI were treated with transfer factor and showed improvement in parameters of CMI and control of their disease.