Natural (estradiol, estrone, testosterone, estriol) and synthetic hormones (ethinylestradiol) are constantly excreted into the environment from human and animal sources but little is known of their transport. The purpose of this study was to determine how far along a 100 km river course that hormones could be detected after contamination with sewage effluent or fishpond effluent. Fourteen sites in the Lower Jordan River drainage were sampled (two sites above the sewage effluent contamination, eight sites below the contamination and four tributaries) before and after the dry season of 2002 (Spring and Fall). Samples were tested for testosterone, estrogen (estrone and estradiol combined), estriol, ethinylestradiol, ammonia and fecal coli. It was found that the fecal coli count dropped exponentially (from 250,000 to 60/100 ml3) and the ammonia dropped from 15 to less than 1mg/l over the initial 25 km stretch. Over the same stretch, the hormone values declined by half from their maximum values for testosterone (3.3 ng/l), estriol (8.8 ng/l), ethinylestradiol (6.1 ng/l), and estrogen (4.9 ng/l). From 67 to 100 km mark, testosterone (4.8 ng/l) and estrogen (2.4 ng/l) were still elevated while ethinylestradiol and estriol were >or=1.5 ng/l. The high level of testosterone and estrogen between 67 and 100 km marks was probably due to major discharge from fishponds between 23 and 27 km marks. Levels of ethinylestradiol above 1 ng/l, a level which can affect fish, was seen in 70% (12/16) of the samples tested. The data suggest that hormones in readily measured quantities can be transported considerable distances from the source of pollution.