The methanol, dichloromethane, petroleum ether, ethyl acetate extracts and volatile components of Spirulina platensis were tested in vitro for their antimicrobial activity (four Gram-positive, six Gram-negative bacteria and Candida albicans ATCC 10239). GC-MS analysis of the volatile components of S. platensis resulted in the identification of 15 compounds which constituted 96.45% of the total compounds. The volatile components of S. platensis consisted of heptadecane (39.70%) and tetradecane (34.61%) as major components. The methanol extract showed more potent antimicrobial activity than dichloromethane, petroleum ether, ethyl acetate extracts and volatile components. Copyright (C) 2004 John Wiley Sons, Ltd.