Résumé : The susceptibility to various antibiotics (penicillins : carbenicillin, piperacillin, ticarcillin ; cephalosporins : cefotaxime, cefsulodin, ceftazidime ; aminoglycosides : amikacin, gentamicin, netilmicin, tobramycin ; colistin) of 462 clinical isolates of P. aeruginosa of serological group 012 from 6 Belgian hospitals (period 1984-1985) has been investigated. Each hospital has used its particular series of antibiotics either by agar diffusion (all hospitals except Liege) or by dilution in microplates (Liege). The 1984-1985 series of isolates, extended to 1986 and completed with some strains from three other Brussels hospitals, was also tested for phage type and pyocin type. Whereas variation of resistance frequency is observed between the different hospitals when antibiotics are considered separately, an overall marked proportion (80 %) of wide antibiotic resistance among 012 strains appears everywhere. A vast majority of our 012 isolates are also characterized by only a few possibility related phage and pyocin types, thus presenting themselves as a fairly homogeneous group. © 1989.