Chicken 7S anti-DNP antibodies requiring a high concentration of salt for precipitation with antigen were purified by immunoadsorption. Difference spectra between free and antibody-bound ligand (ε-DNP-L-lysine) showed maxima at 392 and 470 nm. These maxima and the Δεm at 470 nm were essentially the same as encountered with mammalian and shark antibodies. Chicken anti-DNP antibody of the 7S class has two combining sites (180,000 daltons) as measured in equilibrium dialysis. The average intrinsic association constant (1.6 × 106 M-1 at 5°C) was not altered by wide variation in salt concentration. The 5S bivalent fragment obtained by pepsin digestion also required the anomalous high salt concentration for immune precipitation.