Wild harp seals are vocally active during the breeding season, and utter 19 kinds of underwater sounds. The functions and sources of the sounds are unknown, but are assumed to be mainly from mature males. The purpose of this study is to document vocalizations of captive harp seals during the year, to determine if the calls of harp seals are produced only by males, as proposed, or if females are also vocally active. About 1,000 calls were recorded from February to December 1996, from captive males and females. Only about half the call types could be identified by published call descriptions and many 'intermediate' call types were found. These findings suggest that harp seal vocal communication relies heavily on structural variation and grading. Blood samples from four mature males were analysed, to describe the testosterone concentrations in blood during and after the breeding season to relate seasonality in vocal activity.