In a consecutive material of 652 E. coli bacteremia 70 episodes (11%) were found in 64 patients with diabetes mellitus. 10 patients had insulin-dependent and 54 had non-insulin-dependent diabetes. The E. coli strains were tested for adhesive properties as mediated by P-fimbriae, a virulence factor in human urinary tract infections. Half of the strains were P-fimbriated with a higher occurrence in women (26/42, 62%) than in men (9/27, 33%). Diabetic patients with a positive urine culture had a higher incidence of P-fimbriated E. coli strains (27/37, 73%) in blood culture than patients with negative or no urine culture taken (8/32, 25%). Furthermore, patients without compromising factors, regardless of their diabetes mellitus, had a higher incidence of P-fimbriated E. coli strains (19/29, 66%) than those with malignancies and other debilitating diseases (6/22, 27%). The high incidence of P-fimbriated E. coli strains in the non-compromised patients may depend on the ability of such bacteria to invade the urinary tract and cause acute pyelonephritis, which often precedes E. coli bacteremia. A lower incidence of P-fimbriated E. coli strains was found in patients with proteinuria prior to the bacteremic episode (10/31, 32%), compared to those without proteinuria (25/35, 71%). No correlation was noted between P-fimbriation and duration of diabetes or serum creatinine. The low incidence of P-fimbriated E. coli strains in patients with proteinuria indicates that nephropathy, or some concurrent complication, predisposes the diabetic patient to bacteremia with low virulent, non-P-fimbriated E. coli.