Abstract A monitoring program for bivalve molluscs contaminated by algal toxins was established in 1992 at different stations along the Atlantic Moroccan shore. The presence of toxicity in bivalve molluscs commercially exploited was tested fortnightly using the mouse bioassay method. Results obtained from this surveillance indicate paralytic shellfish poisoning is responsible for bivalve molluscs contamination along the Atlantic coastline of Morocco. Toxin profile was established by automated pre-column HPLC/FLD in selected contaminated tissues. The study of individual toxins in mussel during a bloom in the northern Atlantic coastline in 1994 showed a very complex profile, typical to that obtained with cultures of the toxigenic dinoflagellate Gymnodinium catenatum isolated from the Iberian region. However, toxin composition of mussels and marine beans from later blooms in the southern Atlantic coastline in 1999 showed a strong resemblance with that of Alexandrium minutum, due to dominance of gonyautoxins 1/4. A minor contamination by G. catenatum due to the presence of decarbamoyl-saxitoxin is hypothesized.