Two men (46 and 26 years) developed an undesirable reaction at the site of i.m. administration of one vial of vitamin B12 ŕ 1000 mg with one vial diclofenac (Veral) in the gluteal area. The 46-year-old patient developed at the site of the i.m. administration within 24 hours a sharply defined livid coloration of the skin markedly painful and with neuralgias into the lower extremity. He recovered within two months. The 26-year-old man developed local pain already during i.m. administration of the drugs. Within two weeks he developed at the site of administration dermal and muscular necrosis without neuralgia. Necrectomy was performed and the patient recovered within 6 weeks. NS is a rare local response to the i.m. administration of drugs, very frequently antirheumatic preparations. The cause has not been elucidated completely. During the last two years at the Dermatological Clinic, Faculty Hospital Hradec Králové two cases were recorded.

        Key words: Nicolau syndrome - intramuscular injection