Cells ofProrocentrum lima, isolated from sediments collected from Rangaunu Harbour,P. lima(a Spanish isolate), andP. compressum, isolated from wrack collected at Ninety Mile Beach, Northland, New Zealand, were cultured and analysed for okadaic acid by high‐performance liquid chromatography (HPLC), using the derivatisation method with ADAM (anthryldia‐zomethane).P. lima(from Northland) was found to be equally toxic as cultures of the known toxic strainP. lima(Spanish isolate), and both strains were toxic toArtemia salina. P. compressumwas not toxic toA. salinaand did not produce okadaic acid.