The in vitro activity of the free acid of cefetamet pivoxil (Ro 15-8075) was tested against 355 clinical isolates, namely enteropathogenic bacteria, glucose non-fermentative gram-negative rods (excluding Pseudomonas aeruginosa) and Legionella pneumophila. Ceftriaxone was included in the study as reference compound. Although the free acid of the orally active cephalosporin was generally weaker than ceftriaxone, it inhibited 88.2% and 94.5% of Enterobacteriaceae and Vibrionaceae at a concentration of 4 mg/l and 8 mg/l or less, respectively. Campylobacter jejuni proved resistant to both compounds. The activity of the new compound against glucose non-fermentative gram-negative rods was generally insufficient to be of promise for broad clinical use. Although the compound was at least twofold more active than ceftriaxone against Pseudomonas acidovorans, Pseudomonas alcaligenes and Pseudomonas cepacia, the former was at least two dilution steps less active than the latter against 14 species of the other less common glucose non-fermentative organisms.