ABSTRACT Reproduction of the tropical spiny lobsters Panulirus inflatus and P. gracilis was studied in Guerrero, Mexican Pacific coast, from February 1979 to May 1980, from samples with bottomset nets and from commercial divers' catches. Lobsters caught with nets were tagged, and some females were recaptured up to 4 times during the study period. The smallest ovigerous females measured 49.4 mm (P. gracilis) and 54.7 mm (P. inflatus) carapace length (CL). Reproductive females of both species were found throughout the year, but analysis of the percentage of reproductive females by size class showed that small lobsters ( 70 mm CL). Females of both species > 70 mm CL were capable of producing at least 3 or 4 broods per year, those from 60-70 mm CL up to 3, and smaller mature lobsters 1 or 2. In addition, females between 65 and 80 mm CL had the highest index of reproductive potential, due to their highest numbers in the population and their number of broods per year. Fishery implications of these findings are discussed.