Three lactating Holstein cows with rumen cannulae were used in a 3 × 3 Latin square arrangement of treatments to study effects of methionine source on ciliated protozoa numbers and volatile fatty acid concentrations in the rumen. Cows were fed total mixed diets twice daily of 60% grain mix, 21% corn silage, and 19% alfalfa hay (dry basis). Methionine hydroxy analog, DL-methione, and sodium sulfate were added on an equal sulfur basis. Experimental periods were 14 d with four rumen samples taken daily on d 13 and 14. Total ciliated protozoa were higher when cows were fed DL-methionine than when fed methionine hydroxy analog or sodium sulfate. Ruminal concentrations of butyric acid and isobutyric acid were higher for the DL-methionine treatment than for analog or sodium sulfate treatments. Isovaleric acid concentrations were also higher in fluid from cows fed methionine compared with cows fed the analog.