Aerobic gram-negative bacillus (AGNB) groin skin carriage was prospectively studied in ambulatory geriatric outpatients: 42 from three nursing homes and 44 from private homes. Initially, 12 (28.6%) Proteeae carriers were in the former group and 3 (6.8%) were in the latter (P = 0.01). At one year, 6 of 7 surviving nursing home carriers remained Proteeae carriers while none from private homes remained carriers (P = 0.007). The annual prevalence of Proteeae carriage was 14 (33.3%) in nursing homes and 4 (9.1%) in private homes (P = 0.008); of non-Proteeae AGNB carriage, the annuyal prevalence was 2 (4.8%) and 4 (11.4%), respectively. Nursing home subjects had similar initial health characteristics; however, by one year, 5 of 12 carriers in contrast to 3 of 30 noncarriers were dead of chronic disease (P = 0.03). These nursing homes included persons with chronic diseases that apparently facilitated Proteeae carriage. Urethral catheters, skin ulcers, and recent antibiotics were not factors.