1. Simple extracts of raw navy (haricot) beans (Phaseolus vulgaris L.) known to be toxic to conventional Japanese quail (Coturnix coturnix japonica) have been fractionated and tested for toxicity by feeding to this species.
2. Of the various fractions obtained during the biochemical purification of the phytohaemagglutinin, only those possessing agglutinating activity were found to be toxic.
3. The final purification stage yielded an homogeneous protein with both agglutinating and toxic properties.