1. Ten local Zebu cows representative of Africanowned cattle in Central Tanganyika, maintained under good African husbandry conditions, were temperatured twice daily over a period of 134 days from 23 July to 3 December, whilst the general meteorological environment was recorded.

2. The period of observations was divided into four parts, during two of which differential planes of nutrition were maintained between two groups of animals, the first and last parts being control periods when the plane of nutrition was common to all animals.

3. The diurnal variation in rectal temperature wasapproximately 99·0–102·5° F., arange of 3·5° F., whilst the atmospheric shade temperature varied about 12° F., from 64 to 76° F. at commencement of observations, and from 71 to 83° F. at the warmest period of the observations.

4. The variation within morning rectal temperatures was greater than that within afternoon rectal temperatures.

5. The low rectal temperatures in the mornings reflected inadequate nutritional level to maintain body temperature, as they were significantly increased by a moderate supplementary ration.

6. Supplementary feeding did not affect the afternoon temperatures.

7. Daily mean rectal temperature of the cows in the morning was verysignificantly negatively correlated with atmospheric temperature.

8. Rectal temperatures of ten cows' temperatures at 2 hr. intervals from 07.00 to 21.00 hr., over a period of 7 days, was positively correlated with direct sun temperatures taken 4 hr. before rectal temperatures.

9. Rectal temperatures were positively correlated with the dew-point in the morning, but were unrelated with the lower dew-point in the afternoon.

10. It is suggested that afternoon temperaturing of experimental animals of local Zebu type under African husbandry conditions might be more informative for clinical purposes than the customary morning temperaturing, owing to the lower variation.

11. It is tentatively suggested that the thermoregulatory system of local Zebu cattle may be regarded as operating a micro-adjustment mechanism to compensate for immediate variations in micro-climate, superimposed on a macroadjustment mechanism to extend the limits of operation of the micro-adjustment in accordance with seasonal trends of the macro-climate.

12. Further data are being collected to clarify these tentative conclusions.