An analysis was made of the horses racing at Prairie Meadows race track in Altoona, Iowa during 1993 to determine the number of entries designated as racing under the influence of phenylbutazone (Bute(RX)), furosemide (Lasix(Rx)) or both medications. In a total of 1379 Quarter Horse entries, 5.7 % raced with no medication, 74.9 % raced on phenylbutazone, 0.5 % raced on furosemide, and 18.9 % raced on both phenylbutazone and furosemide. In a total of 3424 Thoroughbred entries, 2.1 % raced under no medication, 43.6 % raced on phenylbutazone, 0.4 % raced on furosemide, and 53.9 % raced on both phenylbutazone and furosemide. Overall, of the 4803 entries, 3.2 % raced with no medication, 52.6 % raced on phenylbutazone, 0.4 % raced on furosemide, and 43.9 % raced on both phenylbutazone and furosemide.