A strict nutritional requirement for lipid and similar components of cell wall fatty acids and sugars are features common to both JK coryneforms (JK) that are resistant to multiple antibiotics and to lipophilic diphtheroids (LD) that are sensitive to antibiotics. We surveyed 123 subjects for LD and JK. Twenty-eight patients with leukemia (776 samples) were cultured longitudinally during 42 hospitalizations; 15 other patients hospitalized for at least two weeks and 80 controls were sampled once. JK were isolated from at least one of four skin sites in 82.1% of the leukemic patients, 73.3% of other patients, and 15.7% of controls. There was an inverse correlation between the density of LDs and JKs in all groups (P = .03). The perineum was the most frequent, and usually the first, site of JK colonization. Once present, colonization persisted for as long as follow-up continued. Systemic vancomycin did not eliminate or prevent skin colonization with JK. Leukemic patients may have a greater risk of JK infection but probably no increased risk of skin colonization.