The relationship between Federal Reserve margin requirements and the behavior of stock prices has long been of interest to academicians and investors. This paper reports the results of a study of price movements around times when margins were changed. Using data from the 1933-69 period, the study concludes that increases in margin appear, at most, to have a trivial depressing influence on stock prices, which takes place over a number of days following the announcement of increases. Margin decreases, on the other hand, do not seem to have any significant impact on price behavior.