Adverse reactions to drugs occur in up to 6% of hospitalized patients and are an important cause of increment in morbimortality. The widely-prescribed antibiotics beta-lactams and sulfamides are the most frequently associated to adverse reactions and hypersensitivity. Vancomycin is a glycopeptidic antibiotic used to treat infections caused by Staph. coagulasa positive (S. aureus) and Staph. coagulasa negative. Nowadays its extensive use is a consequence of bacterial resistance to classical antibiotics such as beta-lactams. In Nephrology Units, vancomycin is the antibiotic of first choice to treat staphylococcal infections related to central venous catheters for hemodialysis, as well as for the treatment of peritonitis in patients undergoing peritoneal dialysis. Toxicity due to vancomycin includes the "red man syndrome", ototoxicity and hematological toxicity. The most common sign of haematological toxicity is mild neutropenia; less frecuent are leukocytosis, eosinophilia, agranulocytosis and thrombocytopenia.