Death from disseminated infection with BCG (bacille Calmette-Guérin) after routine vaccination is rare, and various immune defects may be responsible. An 18-year-old boy died with widespread lymph-node, bone, lung, and liver involvement 6 years after BCG vaccination. Total numbers of B lymphocytes and T lymphocytes were normal, but T lymphocytes, while transforming normally in the presence of non-specific mitogens, did not transform in the presence of purified protein derivative. Delayed-type hypersensitivity skin tests were negative. Monocytes containing alpha-naphthylacetate esterase were absent.