Polycyclic musk fragrances are common additives to many consumer products. As a result of their widespread use and slow degradation rates, they are widely found in aquatic environments. This study reports on the lethal and sublethal toxicity of the polycyclic musks AHTN (Tonalide??) and HHCB (Galaxolide??) to glochidial (larval) and juvenile life stages of the freshwater mussel Lampsilis cardium (Rafinesque, 1820). In glochidia, 24-h median lethal concentrations (LC50s) ranged from 454 to 850 ??g AHTN/L and from 1000 to >1750 ??g HHCB/L (water solubility). Results for 48-h tests were similar to the 24-h tests. In 96-h tests with juveniles, we did not observe a dose-response relation between mortality and either musk. However, the growth rate was reduced by musk exposure. The median effective concentrations (EC50s, based on growth) were highly variable and ranged from 108 to 1034 ??g AHTN/L and 153 to 831 ??g HHCB/L. While all adverse effects occurred at concentrations that are much greater than those reported in natural waters (low ??g/L to ng/L), these results indicate the potential for adverse effects on these long-lived organisms from exposure to synthetic musk fragrances. ?? 2006 Springer Science+Business Media, Inc.