A battery-powered and horizontally positioned clock was modified to automatically present a unique section of dark and wet substrate upon which the malaria mosquito, Anopheles gambiae s.l., could oviposit at hourly intervals over 12 h. The clock face was filled with wet, black agricultural soil covered with removable brown paper toweling. A circular plate of thin plastic was attached to the hour-hand drive of the clock so that all ovipositional substrate was covered except for the equivalent of one hour. The clock turned this panel one revolution per 12 h in the presence of 30 - 60 house-caught gravid females deployed in a 60 x 60 x 60 cm screened cage held under the natural light cycle for equatorial Kenya. Deploying two 12 h clocks sequentially permitted assessment of ovipositional frequency over 24 h. Two discrete periods of oviposition were documented by summing eggs laid per h over seven experimental runs. Of the 12,000 total eggs recovered, 61% were laid during Period 1, beginning at dusk, peaking at 19-20:00 h, and ceasing at 1-2:00 am. Thereafter, no eggs were laid until dawn, when a second ovipositional period commenced that accounted for 39% of the total eggs. Period 2 peaked at 8-9:00 am and continued until noon when mosquitoes were held in the shade. PCR analysis is underway to document whether these ovipositional peaks are shared by or unique to Anopheles gambiae vs. arabiensis.