Organisms. The strains used were : Streptococcus durans (~~1~662, ~~1~8587, NCI~8782, NCTC8307, and two additional strains isolated from pigs) ; S. faecalis var. faecalis (~~1~775, seven additional strains isolated from chickens, and two from humans); S. faecalis var. liquefaciens (12 strains isolated from chickens, five from humans and one from a sheep); S. faecalis var. zymogenes (eight strains isolated from chickens and three from humans); S. faecium (26 strains isolated from chickens, ten from humans and two from pigs). Approximately two-thirds of the test organisms originated from the laboratory collection of Dr E. M. Barnes; the remainder were freshly isolated from either chicken caecal samples or samples of human faeces and identified as described by Sharpe, Fryer & Smith (1966). Cultures were maintained at ambient temperature in cooked meat medium. Test media were inoculated from overnight aerobic cultures in Difco heart infusion or brain-heart infusion medium (see below) and incubated at 37 "C. Breakdown of uric acid. Initially cultures were streaked on double-layered agar plates incorporating a I yo (w/v) suspension of uric acid (Sigma) in the upper layer and 0.1 yo in the lower layer (Schefferle, 1965; Barnes, Mead, Barnum & Harry, 1972). Positive strains pro- duced zones of clearing in the suspended uric acid within 10 days at 37 "C. However, the following method generally gave more rapid positive results and required less uric acid in the test medium. Each strain was streaked on two agar slopes of the following basal medium, one containing 0.2 % (w/v) of uric acid and one without : Difco Tryptone, I yo ; Difco yea& extract, 0.5 yo; glucose, 0.05 yo; phenol red, 0.0012 Yo; New Zealand agar 1-2 %; pH 7-2. The slopes, comprising 10 ml of medium in 19 x 150 mm test tubes plugged with cotton wool, were incubated under H, in an anaerobic jar. After incubation for up to 7 days, the two cultures of each strain were compared and any difference in colour was noted. Fermentation of the small amount of glucose in the basal medium produced an acid (yellow) reaction. This was rapidly followed by the develop- ment of alkaline conditions during the breakdown of uric acid and a change in the colour of the indicator to cherry red.