In connection with an outbreak of atypical shellfish poisoning in Canada due to consumption of mussels from Prince Edward Island in late 1987 and early 1988, an elemental analysis of domoic acid-contaminated mussels harvested during the epidemic was undertaken using the proton induced X-ray emission technique. For this analysis, 30 MeV protons were used to induce K X-ray emission from all elements present above chlorine in the periodic table. A Si(Li) detector was used to detect the lower energy K X-rays and an intrinsic germanium detector to measure As and above. Observed concentrations of several elements were much higher than normal and at a level known to induce toxicity in other bivalved mollusks. Traces of certain heavy elements were also detected. The influence of trace metals on domoic acid toxicity is currently being investigated in our laboratories.