BCG-osteomyelitis is a rare but serious late complication of BCG-immunisation. Be present clinical and immunological findings in 2 children aged 9 months and 5 years, who developed BCG-osteomyelitis, following immunisation with BCG-vaccine. The affected bones were the first metacarpal bone in one and the 6th rib in the other patient. Both children remained free of recurrences after surgical removal of the granulomatous tissue. Immunological investigations in both cases demonstrated normal humoral immunity (Complement CH50, C3, C4, immunoglobulins). Except for a diminished proportion of circulating B-cells, determination of lymphocyte subpopulations and in-vitro lymphocyte stimulation with Phytohemagglutinin and PPD were normal. In both children spontaneous cell mediated cytotoxicity (SCMC) against the tumor cell line L1210, in one patient also against tumor cell line K562 was decreased. Antibody dependent Cytotoxicity (ADCC) was normal.