Abstract We investigate gender differences and menstrual cycle effects in first-price and second-price sealed-bid auctions with independent private values in a laboratory setting. We find that women bid significantly higher and earn significantly less than men do in the first-price auction, while we find no evidence of a gender difference in bidding or earnings in the second-price auction. Focusing on the first-price auction, we find that, while the gender gap in bidding and earnings persists over the entire course of the menstrual cycle, bidding of contraceptive pill users follows a sine-like pattern throughout the menstrual cycle, with higher than average bidding in the follicular phase and lower than average bidding in the luteal phase. In comparison, pill non-users have a flat bidding profile throughout the cycle.