The relationship between level of deprivation and post-reinforcement pause length was investigated in such a way that the nature of the mathematical function which describes the relation could be determined. Three male, albino rats were tested on fixed-ratio schedules of reinforcement at three levels of deprivation, according to the method of adjusted-percentages. Problems with the weight maintenance procedure necessitated changes in the design and may have affected the results. The initial hypothesis, that the function would be of the form Y=bXn, was not supported in any case. A function of the form logY=a+bX was found to best describe the relationship between rats' absolute body weight and the length of the post-reinforcement pause. Conclusions were centered around the need for further research on the effects of long-term deprivation on rats' growth and subsequent reexamination of the relationship under investigation in this thesis.