Evaluation of lymphocyte phenotype frequencies, functional responses, serum immunoglobulin levels, and autoantibodies was completed for 38 individuals (i.e., 10 families) who were exposed to pentachlorophenol (PCP) in manufacturer-treated log houses. Comparison of subjects with controls revealed that the exposed individuals had activated T-cells, autoimmunity, functional immunosuppression, and B-cell dysregulation. Autoimmunity was evidenced by elevation of TA1 phenotype frequencies and a 21% incidence of anti-smooth muscle antibody. Functional immunosuppression was evidenced by the significantly reduced responses to all mitogens tested and to allogeneic lymphocytes in the mixed lymphocyte culture test. There was a significant elevation of CD10, and an 18% increase or decrease in serum immunoglobulins was noted. A striking anomaly was the enhanced natural killer activity found in exposed females but not in males.