We measured the reproductive steroids testosterone and progesterone in free-ranging adult echidnas over several years. For months other than June–August, the mean progesterone concentration was 0.18±0.12ngml −1 (n=14), and all blood samples taken from active female echidnas in June–August had progesterone concentrations above 0.5ngml −1 . The highest progesterone value measured was 13.4ngml −1 in a pregnant female several days before egg-laying. For months other than June–August the mean testosterone concentration was 0.09±0.05ngml −1 (n=13). During June–August all active sexually mature males had testosterone concentrations in excess of 0.2ngml −1 and were found in mating groups at some time during this period. The highest plasma testosterone concentration measured was 4.62ngml −1 .