Behavioral and physiological correlates of vernal reproduction and molting were investigated experimentally in laboratory-held spiny lobsters (Panulirus argus Latreille) from Florida to determine their control by photoperiod and temperature. Behavioral measures included courtship, copulation and aggression; physiological measures included the timing and frequency of ecdysis, spermatophore emplacement, oviposition, egg hatching, and setal (pleopod) and gonadal development. Behavior resembled that observed in nature, as evidenced in the expression of complete reproductive cycles. Long daylengths and warmer temperatures enhanced courtship, spawning frequencies, and female gonadal development, although gonadal recrudescence occurred in large females irrespective of photoperiod. A significant interaction effect between photoperiod and temperature indicated a need to examine joint, non-independent factor effects upon reproductive parameters. Photoperiod and temperature did not significantly influence aggression and male gonadal development. Photoperiod did not affect molting rates significantly. However, warm temperatures enhanced molting and growth such that sub-adult and young adult lobsters (both sexes) had highest molting rates, followed by large adult males, which in turn had higher rates than reproductively active females. Female setal development correlated positively with female size, and changed abruptly at ecdysis. Although setal lengths were highly variable, setae of 9 mm or more signified sexual maturity. Reproduction and molting were size-dependent: the largest adults mated or spawned, the smallest molted, and intermediate-sized ones either mated, or molted before mating. Spiny-lobster reproductive and molting patterns were influenced by photoperiod and temperature in a complex manner depending upon sex, season, size and developmental state.