Fifty-six field isolates ofFusarium solanifrom cucurbits, lucerne, and pens were testel for their pathogenicity on seedlings of their respective hosts and on fruit ofCucurbitaspp. Mating behaviour, including the sex (male (M) or female (F) or both), mating type (MAT1-1 or MAT1-2), and mating population (MP) was examined for 49 of these isolates by maling with known tester strains. Five cucurbit isolates were identified as MPI and five others as MPV. Nine pea, five lucerne, and one red clover strain were identified as members of MPVI. The remaining 24 isolates tested for mating behaviour were unable to mate with any of the testers used. There was clean evidence of host specificity of isolates in the seedling pathogenicity tests. For example, most isolates from peas showed moderate or strong pathogenicity to peas, weak or non-pathogenicity to lucerne, and non-pathogenicity to cucurbits. Cucurbit isolates were non-pathogenic or weakly pathogenic on peas and either non-pathogenic (MPV and non-mating strains) or strongly pathogenic (MPI strains) on cucurbits. Regardless of their host-specificity in the welling tests all strains in a representative sample from the three hosts were capable of producing lesions on wound-inoculated fruits of theCucurbita maximaF1 hybrid buffercup squash ‘Delica’, with over 90% of strains showing moderate or strong pathogenicity. Less than a third of the cucurbit isolates however, showed moderate or strong pathogenicity to unwounded fruit ofCucurbita moschata‘Waltham’. These results indicate that the ability to invade through the intact cuticle and epidermis is a major determinant of specificity.