Antibiotics and hormones are considered emerging environmental microcontaminants because of their potential adverse effects on ecosystems and human health. Available information on the source of these emerging contaminants in surface waters is very limited. The objectives of this study were to determine the occurrence of antibiotics and hormones in an agricultural watershed and to determine the seasonal variability of these contaminants. Water samples were collected from 15 subwatershed stations and 7 stations on the major receiving river, Choptank, Maryland, USA, over four different seasons (April, June, September and December). Antibiotics (sulfathiazole, sulfamerazine, sulfamethizole, sulfamethazine, sulfachloropyridazine, sulfamethoxazole, sulfadimethoxine, tetracycline, oxytetracycline, chlortetracycline and doxycycline) and hormones (estriol, estradiol, 17 alpha-ethynytestradiol, estrone, testosterone and progesterone) as well as arsenic which is used as feed additive were determined in these water samples. In addition, the same antibiotics were analyzed in one set of sediment samples. This study indicated that agriculture may act as a source of antibiotic residues in the aquatic environment.