Ison and Kniaz ( 1963) have concluded that their results and those of Wike and Barrientos (1957) were due to the rat's preference for a drinking tube with a 4-mm. aperture rather than to tubes with larger and smaller apertures. This conclusion is not, however, in accord with the results of Hellyer (1954), who found faster starting speeds in a runway for Ss running to a drinking tube with a 1-mm. aperture than for Ss with 4-mm. one. Hellyer, who used reward magnitudes 0.1 cc. and 1 cc. in combination with these rwo aperture sizes, observed that performance was directly related to duration of consummatory behavior. These various conflicting results suggest the need for some specific studies. First, parametric studies of aperture size and amount of reward are needed to assess the possibility of an interaction between these variables. And second, although we have observed consistent results from studies using the differential (Wike & Barrientos, 1957) and absolute methods (Barrientos, 1957) of reward presentation, further study of this problem is in order.