The heart rate of unrestrained blackbirds Turdus merula was measured in the laboratory by means of radiotelemetry. Tape playback of seven different conspecific song strophes was presented to male and female birds. In addition the plasma titers of testosterone and 7ß-oestradiole were measured in both one male and one female. The heart rate responses (amount of acceleration) varied throughout the year. The males responded most strongly in spring, the females did so in winter. The seasonal response patterns of the males were similar to the pattern of the testosterone titer. The results indicate that conspecific song strophes have different meanings to male and female blackbirds in different seasons.