Description: This paper was presented at the 1957 Society of Actuaries Eastern Spring Meeting, held March 21-22 in New York. The authors present the results of the fourth in a series of mortality studies of the experience of industrial policyholders of the Metropolitan Life Insurance Company for successive periods since 1911. This report extends the series to 1955, with emphasis on mortality trends during the post war decade. Like the earlier reports covering the four decades ending with 1950, mortality trends among these insured lives for the more important causes of death according to age, sex, and race are presented. From Transactions of Society of Actuaries 1957 Volume 9, Number 24.