The antimicrobial activity of silver sulphadiazine has been determined against 409 strains from 12 different genera. MICs were usually in the range 16-64 μg/ml. Multi-resistant species, such as methicillin-resistant Staphylococcus aureus and Acinetohacter spp., were uniformly sensitive. MICs always exceeded the reported aqueous solubility of silver sulphadiazine. No resistant strains were found, and there was no correlation between MIC of silver sulphadiazine and resistance to sulphonamides. Time-kill experiments showed that sulphon-amide-resistant S. aureus (but not Staphylococcus epidermidis) were killed significantly more slowly than were sulphonamide-sensitive strains.