In view of the alleged effect of humic acid (HA) on growth plate arthrosis in humans, we sought to find if poultry tibial dyschondroplasia (TD) is caused by HA that can occur as a ground water contaminant. In 2 separate trials, broiler chickens were fed different concentrations of HA added to their diet for 4 and 5 wk. The effects of these treatments were measured by general health indices such as growth, feed conversion ratio, relative organ weights, blood differential count, serum chemistry, TD index, and bone biomechanical strength. Humic acid treatment decreased BW but appeared to improve feed conversion ratio. There was no effect on TD index or bone biomechanical strength in HA-treated birds compared with controls. There was no toxic effect of HA that was evident by the absence of any dramatic change in relative organ weights or other telltale signs of serum clinical chemistry that would suggest liver, muscle, or kidney dysfunction. Red blood cell, white blood cell, monocyte, and hematocrit values were not affected, but there was a decrease in blood heterophil counts and heterophil to lymphocyte ratio, which was significant in 4-wk HA-treated birds. Overall these results show that HA slows down growth, but it does not have any adverse health effects on chickens.