The fungicidal properties of purified CAY-1, dissolved silver ion and ethylenediamine tetraacetic acid (EDTA) separately were studied in vitro as were the abilities of silver and EDTA to enhance CAY-1 fungicidal properties. Non-germinated and germinating conidia of Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Fusarium verticillioides (Fusarium moniliforme), Fusarium oxysporum and Fusarium solani were incubated separately with CAY-1 (0-24.8 μg ml(-1)), silver (0-111.1 μg ml(-1)), and EDTA (0-2400 μg ml(-1)). Controls consisted of non-germinated or germinated conidia in test medium. To assess combined activity, compounds, based on the sub-lethal doses of each as defined in the initial experiments, were combined and tested in bioassays. Controls for the mixed sets consisted of non-germinated or germinated conidia only or with the sub-lethal CAY-1 test concentrations. The minimum inhibitory concentrations (MICs) for CAY-1 and silver, both separate and combined, were determined. Viability assays showed CAY-1 activity only against the germinating conidia of A. flavus, A. niger and F. solani. Silver was active against the germinating conidia of all fungi and the non-germinated conidia of F. oxysporum and F. solani. Combined silver and CAY-1 produced significant viability loss at concentrations not effective separately. EDTA was not fungicidal separately and did not enhance CAY-1 fungicidal properties. MIC data showed that CAY-1 plus silver had an additive effect. Results indicate that dissolved silver was fungicidal in vitro and enhanced the fungicidal properties of CAY-1 at concentrations ineffective when tested separately.