We present here the first description of harmful and non-toxic red-tide dinoflagellates of the Annaba bay (Algeria), during 2002. The qualitative and quantitative phytoplankton analyses reveal the presence of eleven dinoflagellates; two species, Alexandrium catenella and Gymnodinium catenatum, are responsible for efflorescences and known to be harmful. Seven species, Dinophysis caudata, D. fortii, D. rapa, D. rotundata, D. tripos, Lingulodinium polyedrum, and Protoperidinium crassipes, are considered to produce a toxin. Two others, P. triestinum, and Scrippsiella trochoidea, have sometimes been associated with blooms. Analyses of physical and chemical parameters show that stations 1 and 2 are eutrophic, whereas station 3 is oligotrophic.