The sex ratio of 100 immature Kemp's ridley turtles (Lepidochelys kempi) captured in Gullivan Bay, Ten Thousand Islands, south-west Florida was determined through radioimmunoassay analysis (RIA) of plasma testosterone levels. We determined the sex ratio to be 1·9F:1·0M, corroborating the female dominance reported from other studies. The mean sizes of female (N=57) and male turtles (N=30) were 40·9 cm (±6·9 SD) and 41·9 cm (±6·2 SD), respectively. There were an additional 13 turtles (41·3 cm±6·5 SD) for which sex could not be determined by this technique. Female-biased sex ratios are not uncommon in reptiles with temperature dependent sex determination. If fecundity is not male-limited, the occurrence of a female-biased sex ratio could enhance the recovery of the endangered Kemp's ridley turtle.