The effect of salmon calcitonin (SCT) on the number of T lymphocytes accumulating in air pouch lining membranes produced on the back of Wistar rats was studied. SCT was given from day 0 through day seven following the air cavitation by daily injections of 2.5-20 micrograms/kg directly into the air cavity. Compared with saline controls, treatment with SCT caused a clear reduction in percentage of T lymphocytes, T helper cells and T non-helper subset in the synovial-like air pouch lining as revealed by FITC-labeled monoclonal antibodies and quantified by flow cytophotometric measurements. This effect may be due to a reduction in local vascular permeability caused by SCT.