Intestinal colonization by members of the family Enterobacteriaceae resistant to cefotaxime was surveyed for 3 years in a hematology-oncology unit. Of 416 patients, 66 (15.9%) were colonized, each with a different strain. The incidence of intestinal carriage was not correlated with cefotAxime consumption in the ward but was strongly associated with individual exposure to cefotaxime.Cefotaxime, a broad-spectrum cephalosporin exhibiting high activity against members of the family Enterobacteriaceae (10) and good beta-lactamase stability (13), is often used as first-line empiric therapy in leukemic patients (4,5,9). It suppresses endogenous intestinal members of the Enterobacteriaceae (8, 18). However, strains of Enterobacteriaceae resistant to cefotaxime (CTX-R) have been described with increasing frequency (2,3,6,12,14,18). We previously showed that intestinal colonization is the major harbinger of gram-negative bacteremia in neutropenic patients with hematological malignancies (17). Consequently, intestinal colonization of these patients by CTX-R strains of Enterobacteriaceae might induce bacteremia caused by these resistant bacteria. This is why, in the present work, we analyzed the epidemiology of intestinal colonization by CTX-R strains of Enterobacteriaceae in a hematologyoncology unit using methods that we previously described (1). We also compared the CTX-R strains of Enterobacteriaceae isolated from fecal samples with those isolated from the blood of patients who developed bacteremia.The study started on 1 January 1981, when cefotaxime was first introduced in empirical antibiotic combination therapy in the hematology-oncology unit of our institution, and ended on 31 December 1983. The number of patients discharged was 1,030 (mean hospital stay ± standard deviation, 12.0 + 2.1 days).Fecal samples were usually obtained twice a week from inpatients with fewer than 102 leukocytes per ,ul. In all, 2,009 fecal samples from 416 such patients (34.7 ± 7.6 patients per quarter) were analyzed. Total members of the Enterobacteriaceae (1) and CTX-R strains of Enterobacteriaceae (18) were counted, as previously described. Student's t test was used for comparison of mean log values of bacterial counts. At least three blood specimens were drawn for culture at the onset of all febrile episodes (fever of >38.5°C for 6 h or more). A total of 3,959 blood culture samples were analyzed. Bacteremia was defined as the recovery of a bacterial strain from one or more blood cultures during periods of fever. All the fecal CTX-R strains of Enterobacteriaceae and blood isolates were biotyped by the API 20E system (API, La Balme les Grottes, France), and the MICs of cefotaxime were determined by the method of Steers et al. on Mueller-* Corresponding author.Hinton agar (16). Susceptibility to amikacin, ampicillin, carbenicillin, cefazQlin, chloramphenicol, colistin, gentamicin, kanamycin, minocycline, nalidixic acid, streptomyrin, sulfamethoxazole, tetracycline, tobramycin, and trimethoprim was determined by the disk-diffusion technique...