As a result of the proliferation of toxic marine dinoflagellates along European coasts and the recent discovery of paralytic poisons in French shellfish, experimental studies were conducted on four species of shellfish from the Brittany coasts. Contamination rates of a culture of toxic Protogonyaulax tamarensis, were determined for Mytilus edulis, Crassostrea gigas, Pecten maximus and Ruditapes philippinarum. Mussels and scallops were very rapidly contaminated showing high toxin accumulation rates, whereas rates for oysters and clams were low. During the decontamination phase, two stages were observed in mussels and scallops: a fast decrease in toxin, of the same order of magnitude as the accumulation, followed by a slow decrease, with the toxic rate remaining above the quarantine level of 80 micrograms/100 g. Toxin analysis, both in the culture and in the shellfish, was performed using high performance liquid chromatography. GTX3 and GTX8/epiGTX8 were the dominant toxins in the early stage of the decontamination phases, whereas GTX2 was the predominant compound during the slow phase of decontamination.