Conventional in vivo assays to determine the relative pathogenicity of yeast isolates rely upon the use of a range of mammalian species. The purpose of the work presented here was to investigate the possibility of using an insect (Galleria mellonella) as a model system for in vivo pathogenicity testing. The haemolymph of G. mellonella larvae was inoculated with PBS containing different concentrations of stationary phase yeasts of the genus Candida by injection at the last pro-leg. Larvae were incubated at 30³C and monitored over 72 hours. Results indicate that G. mellonella can be killed by the pathogenic yeast Candida albicans and by a range of other Candida species but not to a significant extent by the yeast Saccharomyces cerevisiae. The kill kinetics for larvae inoculated with clinical and laboratory isolates of C. albicans indicate the former class of isolates to be more pathogenic. Differences in the relative pathogenicity of a range of Candida species may be distinguished using G. mellonella as a model. This work indicates that G. mellonella may be employed to give results consistent with data previously obtained using mammals in conventional in vivo pathogenicity testing. Larvae of G. mellonella are inexpensive to culture, easy to manipulate and their use may reduce the need to employ mammals for routine in vivo pathogenicity testing with a concomitant reduction in mammalian suffering.