A vehicle-mounted net was used on 15 nights during June 1990 and 1991 in northern Oman to collect sandflies in order to identify potential vectors of visceral and cutaneous leishmaniasis. A total of 2216 sandflies was collected comprising four species of Phlebotomus and three of Sergentomyia. Catches were made every 30 minutes between 17.00 h (2 hours before sunset) and 07.00 h (1.5 hours after sunrise). Very few flies were caught before sunset. Most flies were caught at light intensities < 0.1 lux (between 20.00 and 0.500 h), but some flight activity, particularly of males and unfed females, continued even up to 07.00 h (50,000 lux, 1.25 hours after sunrise). Females of the two most abundant species, Phlebotomus alexandri Sinton and Sergentomyia clydei Sinton were significantly more active during the first half of the night (19.00-01.00 h), but males were not. Males of S. clydei showed no clear activity pattern, while males of P. alexandri had two peaks with a decline in activity around 01.00 h. Sergentomyia tiberiadis Adler & Theodor and S. fallax Parrot similarly showed different activity patterns for the two sexes. The circadian activity of females of P. alexandri and S. clydei changed during their gonotrophic cycles. Thus unfed and gravid P. alexandri had two activity peaks during the night, but the blood-fed females were most active during the first half of the night. S. clydei activity was similar, except that the gravid flies, like the blood-fed, had an early peak of activity. Too few parous females were collected to show any clear difference in activity from the nullipars.