The experiments were conducted with 30 male albino rats, each weighing between 300 and 320 grams, at the University of Zurich in Switzerland. Three groups of ten rats each were formed and all rats were killed by either overdose. Rigor mortis was measured by determining the force necessary to cause a 4-millimeter movement of the hind limbs. The first group was held at a temperature of 6 degrees centigrade; and measurements were made at 1, 3, 5, 8, 12, 16, and 24 hours post mortem, plus every 12 hours up to 216 hours post mortem. The second group was held at 24 degrees centigrade; and measurements were made at the same intervals through 24 hours post mortem but not later. The third group was held at 37 degrees; and measurements occurred at 1, 2, 3, 4, and 6 hours post mortem. The relative humidity (air) was 60 percent for all groups. The results showed that for the first group, rigor mortis reached full development between 48 and 60 hours post mortem and was resolved at 168 hours post mortem. The second group reached full development at 5 hours and was resolved at 16 hours and the third reached full development at 3 hours and was resolved at 6 hours. In addition, a 'cold rigidity' was found to set in at 6 degrees centigrade, in addition to and independent of rigor mortis. Generally, the intensity of rigor mortis was shown to grow with increases in temperature. Considering the great similarity of mammalian muscle tissues, the study assumes that these results are directly valid for humans. Data tables and graphs and a 14-item reference list are included.