Cephalosporins are bactericidal antibiotics that are active against a wide variety of Gram(+) and Gram(-) aerobic bacteria, along with a few anaerobic species. Adverse effects of cephalosporins are uncommon and reversible. Cefalotin and cefaloridine exhibit a nephrotoxic effect and might cause renal tubule necrosis. No data about the nephrotoxicity of cefotaxime and ceftriaxone has been presented in literature so far. When cephalosporins are applied via intramuscular injection a local reaction is possible, whereas with IV administration thrombophlebitis develops in about 5% of all cases. Hypersensitivity reactions, as well as some hematological disorders (thrombocytosis, leukopenia, neutropenia) might also occur. Cephalosporins were found to sometimes cause an augmentation of transaminase (AST, ALT), alkaline phosphatase, and, less frequently, bilirubin levels, too. The goal of this study was to evaluate the creatinine values in the serum of patients hospitalised in Kosovska Mitrovica Health Centre. The values were determined before, within and after 7 days of cephalosporin administration (cefotaxime 2x1000mg IM; ceftriaxone 2x1000mg IV). Data concerning certain hematological and biochemical variables will be presented as well. Creatinine levels were measured by the Jaffe reaction method. Both cefotaxime and ceftriaxone yielded a statistically significant increase of the serum creatinine values. As these cephalosporins do not show a nephrotoxic effect, the increase can be explained by the interference of sodium picramate, a byproduct of the Jaffe reaction which is produced regardless of whether the process is manual or automated.