We tested the possibility of measuring proges-terone levels in bubbler samples collected from free-rang-ing live bottlenose dolphins (n = 11) and long-Wnned pilot whales (n = 2) as a tool to evaluate the pregnancy status of individuals. Samples were collected during January 2004 and September–October 2005 in the Strait of Gibraltar and Gulf of Cadiz and used for sex-determination by genetic methods (skin samples) and for quantiWcation of progester-one levels by enzyme immunoassay. Photo-identiWcation tracking of females after taking the biopsy was used to observe the presence of newborns and, in this way, to deter-mine if the female was pregnant at the time of sampling. Mean progesterone levels from pregnant bottlenose dolphins (n = 2) were around 9 times higher than those from non-pregnant females (n = 9), with no overlap between concentration ranges demonstrating that this method could constitute an eVective tool for determining pregnancy in wild populations of bottlenose dolphins and other cetacean species.