Four White Carneaux pigeons were trained to respond for food on concurrent variable interval reinforcement schedules. Their weights were systematically established at 73%, 80%, 87%, and 94% of ad lib, As weight increased, relative response rate and the relative time spent in the more dense schedule remained constant, while post reinforcement pause increased. There was less variation in time allocation than response ratios_The effect of different levels of food deprivation on relative and absolute response rates has received considerable experimental attention (cf. Bolles, 1967). After depriving three groups of rats for up to 23 h, Clark (1958) reinforced each according to a different variable-interval (VI) schedule. Response rates increased with increased deprivation time, but the ratio of responses between the various schedules remained constant over deprivation conditions. Dinsmoor (1952) developed the ratio of responses made during the reinforcement component to responses made during the extinction component of a multiple schedule. The absolute rates of responding increased systematically in both components as deprivation (measured as percentage of free-feeding weight) increased. But, once again, there was no change in the ratio of response rates between reinforcement and extinction periods.Powell (1973), on the other hand, has suggested that the degree of stimulus control over a pigeon's behavior, in an experimental situation, determines the in variance of the ratio of the response rates. Under conditions similar to Dinsmoor (1952), Powell showed that response in extinction, relative to reinforced responding, changed as deprivation increased when stimulus control was weak_ The response ratio was not affected, however, when stimulus control was strong. This constancy of response ratios (under conditions of strong stimulus control) over changes in deprivation levels is provocative, for it is just such invariances that provide leverage in the construction of general laws of behavior. This particular invariance suggests that behavior ratios (cf. Herrnstein, 1961;Tolman, 1951) may provide an index that is robust in the face of changing deprivation levels, even within the course of an experimental session (Lydersen & Cheney, 1973), More importantly and for many purposes, such a measure avoids the difficult, if not insoluble problem of equating deprivation levels across species.In the context of concurrent reinforcement schedules, the behavior ratio has been the dependent variable of choice (see, e.g_, Baum and Rachlin, 1969; Rachlin,The authors wish to thank G. Opfer, M. Newsom, and, especially, P. Killeen for suggestions on earlier drafts of this paper_ This study was conducted while the first author was a Master's Degree candidate at Arizona State University. 4 1971). But it has never been clearly demonstrated that the behavior ratio in concurrent schedules (Le., the rate of responding on one schedule divided by the rate on the other) is invariant over deprivation level. The issue of deprivation invariance is...