The gonyaulacoid dinoflagellate Alexandrium taylori Balech is reported for the first time from Italian waters. In July 1997, nonmotile stages of this species, both temporary and sexual resting cysts, were found in surface Ionian coastal waters (Mediterranean Sea) producing localized brownish-yellow patches. Clonal cultures were established, and the life history of A. taylori was studied in the laboratory. Asexual reproduction took place during a motile phase and produced two daughter cells remaining temporarily attached in pairs. This species exhibited isogamy. Small gametes were produced from vegetative cells through the release of a division cyst and multiple fission of the protoplast. Isogametes from the same clonal strain fused and underwent sexual reproduction, forming planozygotes that subsequently developed storage bodies and dark pigmentation. The maturation of the planozygote into hypnozygote also involved an increase in size and final shedding of flagella and theca. Hypnozygotes germinated within 15 days of their formation, and a naked planomeiocyte emerged from the archeopyle to undergo successive divisions and reestablish a haploid motile population.