The effects of cadmium and copper on larval metamorphosis and mortality of cultured Capitella sp Y were investigated. Metatrochophore larvae were exposed to 0.013 (control), 0.030, 0.080, 0.120, and 0.170 mg Cd L−1 and 0.017 (control), 0.025, 0.060, and 0.075 mg Cu L−1 for 34 days. Larval mortality significantly (p < 0.01) increased with increasing Cd and Cu concentrations (Kruskal-Wallis test), with similar effects for both metals for day 10 (LC50 = 0.035 mg Cd L−1 and 0.035 mg Cu L−1). Metamorphosis was inhibited in larvae exposed to the two metals in the absence of food, the effect of Cu being the most severe. This study suggests that Cd and Cu exposure could be harmful to early developmental stages of Capitella sp Y producing a delay in recruitment into natural populations.