From the caeca of 252 horses, 503 sheep, 250 goats and 250 swine, 486 yeast isolates belonging to 28 species and 1 variety were obtained. The distribution of the yeasts of any species and for Candida albicans respectively was: horses, 52·4%, 4·4%; sheep, 6·8%, 4·2%; goats, 6·4%, 0·8%; swine, 88·8%, 9·2%. The suitability of the sheep and goats as hosts for yeasts of any species seems very limited. The most frequent occurrences for single species were: Candida slooffii in swine (48·4%), Trichosporon cutaneum in horses (21·8%) and Saccharomyces tellustris (Candida bovina) in swine (14%). One isolate of Cryptococcus neoformans was obtained from a healthy horse, suggesting that horses might sometimes contribute to the dispersal of this pathogen. Temperature relations, vitamin requirements and some assimilative properties of the following organisms were determined (total number of isolates in brackets): Saccharomyces tellustris (3), Torulopsis glabrata (6), T. pintolopesii (10), Candida bovina (6), C. slooffii (6), Cryptococcus neoformans (23) and Trichosporon cutaneum (12).