Invasive infections caused by bacteria and fungi are common complications of intravenous drug abuse. Various vital organs and structures may be affected, e.g. the cardiac valves, the larger arteries, the bones, the joints and the central nervous system. However, due to the high frequency of low-virulent microbes of skin and oral origin, the clinical picture may be atypical with subacute course and few focal signs and symptoms. The complexity of this problem is illustrated by eight cases of serious bacterial and fungal infections recently diagnosed at our hospitals. All patients were HIV negative intravenous heroin addicts. The clinical spectrum was wide and included skin abscesses, pyomyositis, spondylodiscitis, septic arthritis, costal osteomyelitis, infective endocarditis, recurrent bacteraemia, and multiple brain abscesses.