In order to investigate the stability of testosterone (T) and androstenedione (Adione) in blood and plasma samples following study was undertaken. 1. Pooled blood samples were left unseparated at room temperature for varying time periods of up to 3 days before being centrifuged. Subsequent plasma T and Adione values measured by radioimmunoassay showed only small, insignificant variations. 2. Plasma, initially separated from the pooled blood sample, was left at room temperature for up to 24 h. There was no significant change in the levels of T and Adione measured over this period. There was also good correlation between steroid concentrations measured in blood and plasma. 3. T and Adione were measured in a pooled plasma sample after repeated freezing and thawing of the sample. All T values were well within the intraassay coefficient of variation; all Adione values were within the precision limits of the assay, although there was a considerable spread in individual values. It is concluded that the various handling procedures of blood or plasma have no significant effect on T and Adione levels.