A high correlation was found in the pattern and in the degree of variation of the pH of the blood among a group of dogs studied over a period of 1 yr. A high statistical correlation was obtained in comparing the continuous pH values in a group of dogs with those of a group of humans for a period of 1 yr. A relatively wide degree of fluctuation was observed in both humans and dogs. In man, the weekly avgs. varied from 7.28 to 7.68; while in the dogs they varied from 7.32 to 7.68. In comparing the pH and the weather, statistically significant coefficients were found with barometric pressure and temp., with a distinctly higher correlation being found for barometric pressure than for temp. Increases in pH were associated with increases in barometric pressure. The relationship between pH and temp. was not as marked and only at higher temps. were increases in pH definitely associated with increases in temp. In attempting to evaluate seasonal influences varying results were found, depending upon the weather indices discussed.