Heavy metal pollution in aquatic ecosystems is a far reaching environmental problem. The possible influences of heavy metal exposure and the potential harm to organisms when combined with other environmental stressors such as temperature have been largely unexplored. An aquatic toxicity test of Caenorhabditis elegans was performed to estimate the 24 h median lethal concentration (LC50) of different zinc concentrations at different temperatures (15 degrees C, 20 degrees C, 25 degrees C, and 30 degrees C). We also examined the time course thermotolerance on wild type (N2) and daf-21 null (JT6130) adults exposed to 6.1 mM zinc at 37 degrees C. Hsp90 protein expression level in response to the combined effect of temperature and zinc toxicity was also investigated by both Western blots and ELISA. Our results show that C. elegans wild type nematodes exhibit severe lethal toxicity after a 24 h exposure to zinc at higher temperatures. In addition, the expression level of Hsp90 was highly inhibited in adult worms subjected to zinc stress. This toxicity assay at different temperatures provides insight into organism response to combined effects of temperature and zinc toxicity.