Six cases of neonatal meningitis due to E. coli (3 cases), K. pneumoniae (1 case), P. aeruginosa (1 case) and S. marcescens (1 case), and eleven cases of suckling and little child meningitis caused by M. influenzae (10 cases) and N. meningitidis (1 case) were treated with ceftazidime. The susceptibility of agents was qualitatively tested according to the disk-diffusion method, and quantitatively according to biological dilution method on liquid broth. Ceftazidime concentrations in cerebrospinal fluid and sera were determined by the modified microbiological method using diffusion on agar. Efficacy of ceftazidime therapy was assessed by quickness of cerebrospinal fluid "sterilization", duration of antimicrobial therapy and outcome of the disease. In spite of very good agents susceptibility to ceftazidime determined by disk-diffusion method, notable differences were found in quantitatively determined susceptibility (minimal inhibitory and minimal bactericidal concentration). Antibiotic penetrability was various in proportion with individual intensity of blood brain barrier break down. Bactericidal effect and prompt "sterilization" of cerebrospinal fluid within 48 hours after the beginning of ceftazidime therapy was achieved in those patients in whom ceftazidime cerebrospinal fluid concentration was 10 and several times higher than the minimal bactericidal concentration (all cases due to H. influenzae, N. meningitidis and E. coli). In these cases the issue of the disease was also favourable and none of the patients died.(ABSTRACT TRUNCATED AT 250 WORDS)