The behavior of three captive specimens of Delphinapterus leucas was observed for prolonged periods and their underwater sound production was recorded. Sonic and physical activities of the whales were correlated, and their sounds are compared with those of other cetaceans. Physical analyses for r epresentative sounds from ro distinct categori es are presented for a 47-minute recording period. Frequency components were measured in the infrasonic, sonic and ultrasonic ranges.