beta-Propiolactone (BPL) inactivates LAV/HTLV III, the retrovirus associated with acquired immune deficiency syndrome (AIDS). Addition to specimens from patients with suspected AIDS or antibodies to LAV/HTLV III could reduce any occupational risk to laboratory staff. This study demonstrates that BPL treatment does not significantly affect the immunological analyses commonly required on these patients, namely measurements of serum immunoglobulins, complement components C3 and C4 and other serum proteins, detection of autoantibodies and estimations of T lymphocyte subpopulations.