The microbial flora of 60 vase water samples from cut flowers obtained from several environments, including a hospital, were examined in this study. Forty-one different bacterial species were identified, including 12 species of Pseudomonas. The mean total aerobic bacterial count per 500 ml of vase water was 4.5 x 10(8) organisms, and high levels of antibiotic resistance were found. To ascertain the origin of the bacteria found on the flowers as well as their growth patterns, natural cut flowers were compared with sterilized cut flowers in tap water over time. Although the density of organisms was similar, the flora in vase water of sterilized flowers consisted almost entirely of aerobic spore formers while mixed flora of gram-negative bacteria, staphylococci, aerobic spore formers, and fungi were isolated from natural flowers. Our results indicate that the multiply-resistant microbial flora found in vase water is indigenous to flowers, rather than originating from the environment in which they are placed, and that such water is a reservoir of large numbers of multiresistant organisms.