The bioactive amides affinin and capsaicin isolated respectively from Heliopsis longipes roots and Capsicum spp fruits, were assayed for activity against Escherichia coli, Pseudomonas solanacearum, Bacillus subtilis and Saccharomyces cerevisicae suspension cultures. The alkamide affinin inhibited growth of E. coli and S. cerevisiae at concentrations as low as 25 microg/ml. Higher concentrations of affinin were necessary to inhibit growth of P. solanacearum and B. subtilis. However. high concentrations of capsaicin only retarded the growth of E. coli and P. solanacearum, whereas growth of B. subtilis was strongly inhibited and that of S. cerevisiae was initially enhanced. Results are discussed in relation to previous reports concerning crude extract and to the molecular structures of the bioactive compounds.