Effects of age and hunger on the pattern of sound production in the tsetse, Glossina morsitans morsitans Westwood were determined. Although an afternoon peak was evident in young flies only on day 1 and virtually absent on all days in mature flies of both sexes, sound production in 12:12 LD basically seemed to follow a ‘U’-shaped pattern typical of other diel responses. Experiments under constant light (LL) and constant dark (DD) conditions did not indicate a clear circadian rhythm associated with sound production. Food deprivation led to a decrease in total daily sound production in contrast to other activities in G. morsitans morsitans.