Absorption of phosphate into single human and animal hair shafts has been studied by means of 32P radiotracer techniques. Nondestructive radioassay permitted repetitive experiments on the same hair specimen. Phosphate concentration patterns were shown to be complementary to those for zinc absorption and sometimes to exhibit prominent concentration peaks extending over regions of the shaft 10 to 20 mm in length. Appearance of such peaks was shown to be favored by pH decreasing below 7 but not by migration of phosphate along the hair shaft, which was unimportant.