A method of assessing erythromycin-resistant strains of Staphylococcus aureus for their susceptibility to the antibiotic clindamycin. Erythromycin-impregnated disks are placed near clindamycin, or lincomycinimpregnated disks on a growth medium, and the effect of inducible erythromycin resistance on the inhibition of bacterial growth around the clindamycin disk is assessed. A flattening of the zone of inhibition around the clindamycin disk is indicative of clindamycin drug resistance.