The effect of rehabilitation at different stages of development of rats marginally malnourished for ten to twelve generations.

1. Rats which have been maintained for ten to twelve generations on diets of low protein value were rehabilitated in utero (group P), from birth (group F) and from 4 weeks of age (group W). 2. Group W showed little change in physique, behaviour or learning, indicating that for recovery to be effective refeeding must begin earlier. 3. Group F just failed to attain full physical recovery (90%) whereas group P overgrew by 18.6% in weight and 8.5% in length. 4. In a test designed to evaluate learning ability rehabilitated rats of groups P and F were significantly less successful than normal rats, but more successful than rats of group W or rats of the original undernourished colony. 5. Rehabilitation for a further two generations in groups F and P corrected any residual physical and behavioural defects but produced no further improvement on the Lashley (1938) jumping platform.