The effects of two concurrently changing drive variables, food deprivation and estrogen level, on the self-stimulation rate in the hypothalamus, septum, caudate nucleus, or dorsal hippocampus of 15 female albino rats were studied. When the effects of hunger were calculated using only scores on days of diestrus and the effects of estrogen were calculated using only scores on days of 0-hr. food deprivation, the correlation of these hunger and estrogen effects amounted to 0.67. When the hunger effects were calculated using only scores on days of estrus and these hunger effects correlated with the previously calculated estrogen effects, the correlation amounted to −0.49. These results are consistent with the concept of diffuse overlapping motivational systems in the brain. Controls indicated that the changes in self-stimulation rate were not artifacts of changes in nonspecific activity.