1. The osmotic ratio between ‘urine’ (the supernatant of the ureteral part of the droppings) and plasma has been determined in a number of dehydrated West Australian birds.
2. The U/P ratio was 1.4 in the Emu, 1.7 in two Columbidae (Senegal Turtle Dove and Crested Pigeon), 2.4 in two Meliphagidae (Singing Honey-eater and Red Wattle Bird), 2.6 in three Psittacidae (Bourke Parrot, 28-Parrot, and Galah), 2.7 in the Laughing Kookaburra, and 2.8 in the Zebra Finch.
3. The Na+ and Cl- concentrations in the ‘urine’ ranged from 5 to 71 m-equiv./l, the K+ concentration from 92 to 201 m-equiv./l.
4. There seems to be a rather narrow range for the concentrating ability within each family, but the concentrating ability of xerophilic birds differs considerably.