1. Repeated platelet counts, 991 in number, were made on 148 adult male rabbits of various breeds and types which were specifically selected on the basis of physical fitness and continued freedom from disease. The observations extended over a 2½ year period (1929–32).
2. A unimodal, peaked, moderately asymmetrical distribution curve was obtained and an analysis of the results gave the following values: the mean, 532,645 platelets per c.mm.; the median, 520,604 per c.mm.; the mode, 503,962 platelets per c.mm. respectively.
3. The extent of the variation among the counts is shown by the standard deviation of 124,960. High platelet counts were found to occur more frequently than low counts, a result that is reflected in a significant skew to the right in the frequency curve.
4. It was calculated that in healthy male rabbits a platelet count of less than 220,000 or more than 845,000 per c.mm. should be considered abnormal.