The urinary alpha1-microglobulin (alpha1-M) as a marker of proximal tubular damage was measured in 86 children, aged 3/12 to 12 years, with a diagnosis of urinary tract infection (UTI) and fever. All patients had normal glomerular filtration rates (GFR). They were divided into 2 groups: A: with UTI and etiological factor E. coli, B: with UTI and etiological factor Proteus sp. Similar measurements of alpha1-M were obtained for a control group of healthy children. An increased mean level serum alpha1-M was observed in patients with UTI and fever compared to control group (p < 0.001). Urinary alpha1-M as the alpha1-microglobulin/creatinine ratio was higher in both tested group of patients with UTI and fever. Those found in group A1 and B1 before treatment were the highest and statistically significantly elevated after treatment (group A2 and B2: p < 0.001). Our results indicate the usefulness of the urinary alpha-microglobulin/creatinine ratio as a marker of proximal kidney tubule damage in children with E. coli and Proteus sp. infections. Additionally, it seems to be associated with the humoral and cellular immune response.