The antibacterial activity of cefminox (CMNX) was compared to those of cefotaxime (CTX) and latamoxef (LMOX) in human urine using 11 clinical isolates from complicated urinary tract infections. When the inoculum size was increased from 10(4) (or 10(3)) to 10(8) (or 10(7)) CFU/ml, MIC values increased in general, but the increment of average MICs of CMNX was the smallest of the 3 drugs: 4 approximately 8 fold with CMNX, 32 approximately 64 fold with CTX and 8 approximately 32 fold with LMOX. MICs also increased when the urinary pH was altered from 8.5 to 5.5, but again the increment of MICs of CMNX was the smallest. Using 5 clinical isolates of Gram-negative bacteria as test organisms, the bactericidal activity of CMNX was compared to those of CTX and LMOX. In spite of the inferior activity of CMNX as determined by the MIC values, CMNX showed killing activity equal to or better than CTX and LMOX, particularly at low concentrations (2 approximately 20 micrograms/ml). The bacteriolytic activity of CMNX was also equal or superior to those of CTX and LMOX against 6 test organisms. These results suggest the usefulness of CMNX in the treatment of urinary tract infections, particularly when dense bacterial populations are present.