We have supernates of cultures of skin fibroblasts from healthy subjects and patients with mycosis fungoides to study for T cell inducing activity. We have serum from a large patient population with different stages and histological types of Hodgkin's disease to bioassay. Similarly, we are scheduled to assay serum from 50 patients with active or inactive Hodgkin's disease. Our bioassay for T and B cell inducing activity in human serum is a novel technique. It permits determinations as to whether disorders involving these lymphocyte series are at the cellular or inductive level. In so doing, it greatly enhances understanding of pathophysiological processes. It also suggests the potential for identifying diseases that might be benefited from thymic hormone administration.