This paper examines the relationship between the variability of profit rates and the size of firms. Two types of variability are investigated. The first is the intra-class variability of these ratios for two specific years, 1955 and 1958. The data indicate that this variability is inversely correlated with size. Profit ratios also vary over time and this type of variability is also examined. The results show that the time variability of the average rate of return for both small and large firms is less than that of medium sized firms. Finally, the paper shows that the results of these two separate investigations are consistent.