Effects of elevated temperature, in combination with exposure to the fungicide fenarimol, on reproduction in the deposit-feeding Baltic amphipod Monoporeia affinis were investigated. Previously, fenarimol was found to cause endocrine disruption in other crustacean species, via the ecdysteroid system. M. affinis were exposed to elevated temperature and/or fenarimol in soft-bottom microcosms during sexual maturation and mating. Elevated temperature and fenarimol (0.7 mg l(-1)) acted synergistically and increased the number of females with dead eggs, with a more than 4-fold incidence compared to exposure to one of the stressors (24 vs. < 5 %). Exposure to both stressors also resulted in a negative intrinsic rate of increase, which might indicate a population decline in the field. Elevated temperature impaired sexual maturation in males and females, lowered the number of fertilised females, reduced fecundity and altered embryogenesis. Exposure to fenarimol resulted in a 40 % decrease in ecdysteroid levels in sexually mature males and an increase in heat shock protein 60 expression. Ecdysteroid levels were not affected by temperature in either sex or stage of sexual maturation. Our results suggest that increase in the water temperature due to, e.g., global warming would impair reproduction and possibly increase the sensitivity of M affinis to toxicants.