Fosfomycin is a new bactericidal broad-spectrum antibiotic. In this study the minimum inhibiting concentration (MIC) was determined for 745 recent clinical isolates. Staphylococcus aureus and epidermidis, group A and B streptococci Streptococcus faecalis and pneumoniae as well as Escherichia coli, Proteus mirabilis, Serratia marcescens and Haemophilus influenzae were very sensitive to the new drug with essentially all strains inhibited at 64 mg/l or less. Klebsiella, Enterobacter, indole-positive proteus and Pseudomonas-aeruginosa were less sensitive with 96, 42, 66 and 58% inhibited at 64 mg/l of fosfomycin. Bacteroides fragilis was resistant.