A study of the distribution of the summed (right plus left) a-b ridge count in 1,000 normal subjects showed a significant deficit of counts at the two ends of the range. In males the distribution was significantly different from a normal distribution, but in females a similar trend did not reach statistical significance. No significant sex difference was found, although it is known that abnormal sex chromosome complements may affect the a-b ridge count. The influence of the sex chromosome complement on the a-b ridge count appears to be smaller than the effect of the sex chromosome complement on the total finger ridge count. The a-b ridge count is probably also less genetically determined than the total finger ridge count.