Temp, measurements were made in the bone marrow of the sternum, iliac crest, tibia, spinous process and vertebral body in 10 patients by means of a thermocouple inserted through a standard bone marrow needle. Temps. ranged from that of the rectum in the vertebral body marrow, to 4% below rectum in the other bones, suggesting the lack of precise temp. regulation of the hemato-poietically-active bone marrow. No correlation between temp. and cell-type was observed.