Facilitating and inhibiting sets were given to 72 human Ss in a classical galvanic skin response (GSR) conditioning situation employing a within-S design. Three groups of 24 Ss each were given 4 UCS adaptation trials followed by 10 acquisition and 16 extinction trials. Three different interstimulus intervals (ISI) were included as a between-S variable. Both acquisition and extinction data revealed that GSR magnitude on facilitatory trials was significantly larger than on inhibitory trials (p< .01). Results further indicated that differential responding in accord with instructional set was not dependent upon an extended es-ues intervaJ.