The diel activity patter n of Glossina austeni was studied on the south coast of Kenya, and in the laboratory. In the field, flies were sampled hourly by continuous catch from a standing vehicle, or by traps. In the laboratory, observations were made of the flies' take-off-responses to host odour at various times of the diel cycle, in a flight chamber. The results showed that G. austeni is day-active with some activity throughut the daylight hours, but with significant peaks occurring at 09.00–10.00h and between 14.00 and 17.00h, i.e. a roughly V-shaped pattern.