SummaryAuthor has studied from a statistical point of view the results obtained in normal people when determining the number of blood platlets by a procedure described by Van Herwerden en Van Goidsenhoven.In 50 subjects of both sexes the following results have been obtained ; average value 269.400 : standard deviation 53.700 : physiological range from 376.800 to 162.000; extreme values 430.000 and 142.000.The average value is the same in men and women.In women however the results are somewhat more spread than in men. This is specially true just before the catamenia.To be significant the difference in two platlets counts has to be larger than 17 % of their mean value.