The relations between concentration, volume per reinforcement, interval between reinforcement, degree and kind of deprivation, and rate of responding for saccharin solutions in the Skinner box were explored. For hungry SS, initial rate of responding increased with concentration and volume, and decreased with interval. No combination of these variables proved to be additive. The slope of the initial rate vs. log concentration function increased with deprivation; the slope of the initial rate vs. log volume function did not. When Ss were thirsty the rate vs. log concentration function became flat at the low concentrations and decreased at the high; the rate vs. log volume function retained the same shape. Rate of shutoff, within a session, was an inverse function of magnitude of reinforcement at low levels of reinforcement and a function of the magnitude of load at high levels of reinforcement. The rate of shutoff seemed not greatly affected by deprivation. The relations found for saccharin were similar to those for sucrose. The implications of the differences between saccharin and sucrose, e.g., osmotic and metabolic, were examined for an account of these relations in terms of the view that a threefold locus of events governs the rate of responding, the proximal reinforcing stimuli, the momentary ingestive load, and the nutritive condition of the animal.