A postmarketing surveillance of cefminox sodium (Meicelin, CMNX) for intravenous injection was conducted for about 4 years from August 1987 through June 1991, and 13,431 patients were followed up to evaluate the safety of the drug. The incidence of side-effects was 1.76%. By organ, the most frequently observed were hepatic and of the bile duct system (0.87%) followed by those on leukocytes and reticuloendothelial system (0.24%), skin and adnexa (0.24%) and digestive tract (0.16%) indicating a tendency similar to that of other injectable cephalosporins. The incidence of the side-effects among elderly patients (65 years old or older) was 2.12%, whereas among patients 64 years old or younger it was 1.58% with no significant differences between the two groups. No side-effects specific to the elderly were observed. Among children 15 years old or younger the incidence was 0.59%, which was lower than that for patients 16 years old or older (1.90%). Potential side-effects on pregnant women (n = 101) and their babies were also checked. No side-effects occurred among the 52 pregnant women evaluated and no abnormalities were detected in their babies who were followed up for up to 4 years. Cefminox is thus considered to be a highly safe cephalosporin antibiotic.