An aqueous extract of Morinda citrifolia was shown to interfere with the serum-induced morphological conversion of Candida albicans from a cellular yeast to a filamentous form in vitro. The conversion of C. albicans from a cellular yeast to a filamentous form in vivo is associated with pathogenicity. No significant effect on growth in serum-free media was seen at the concentrations used to interfere with the morphological change. The same extract also inhibited the germination of Apergillus nidulans spores. These results demonstrate that M. citrifolia contains a water-soluble component or components that interfere with the morphological conversion of C. albicans and the germination of A. nidulans and may have potential therapeutic value with regard to candidiasis and aspergillosis.