1. The exponential removal of ICG from the plasma by the mallard duck liver made possible the measurement of fractional dye clearance (K), plasma volume (PV) and plasma clearance (PC).
2. Values obtained for K (14.9%/min), PV (39.2 ml/kg) and PC (5.8 ml/min per kg) agreed with those obtained by other techniques used in a number of species.
3. Sex did not affect the removal of ICG by the liver. However, increases in K, PV and PC were noted in hen mallards in laying condition.
4. The data should prove useful as baseline values for physiological and pathological studies on the avian liver