Data on activity patterns of the desert nightsnake (Hypsiglena chlorophaea) were obtained from 121 specimens. Hypsiglena chlorophaea was active on roads in central Washington during April–October. Specimens were collected at temperatures of 9.1–40.8°C. Males were collected more frequently than females during May, but in equal numbers during June and July, while more females were found in August–September. Hatchling snakes were collected in July–September. Hypsiglena chlorophaea was active 2100-0500 h. Snakes were collected more often during periods of low moon-light (e.g., new moon) than high moon-light (e.g., full moon).