R. Alton Gilbert describes the two measures of banking system reserves published by Federal Reserve sources and analyzes why their growth rates often differ substantially over periods of a few months. He shows that differences between growth rates of the reserves series published by the Federal Reserve Bank of St. Louis and by the Board of Governors often reflect simply the different methods used in adjusting the reserve series for seasonal influences. At times, however, differences in methods of adjusting for the effects of changes in reserve requirements and differences in the treatment of vault cash as reserves have contributed to the short-run differences in growth rates observed in the past.