The interactions between lymphocytic choriomeningitis virus-specific cloned cytotoxic T lymphocytes (CTL) and virus infected targets have been examined by electron microscopy. CTLs, which were readily differentiated from target cells by the presence of cytoplasmic granular inclusions, made intimate contact with infected cells. Some CTLs contacted infected cells via numerous interdigitating processes; others were observed thrusting finger-like protrusions deep into the target cell; some were seen with their plasma membranes lying closely opposed to that of the infected cell. The majority (55%) of bound CTLs had their Golgi apparatus oriented towards the target cell and 42% of bound CTL had granular inclusions in close proximity to the contact zone. Evidence is presented which suggests that the contents of the granular inclusions are released by CTLs in contact with infected cells. Granules appeared to be released close to the target cell rather than from random sites on the CTL surface. Examination of supernatants from effector-target cell incubation mixtures by negative staining revealed membranes bearing lesions with an internal diameter of approximately 15 nm.