6 groups of 12 albino rats received 80 acquisition trials, defined as 12 bar-presses, with sucrose reward. Two groups received 100% reward; four groups received 50% reward, half with a dipper click on all trials (50C), half with a dipper click only when reinforced (50C-NC). 3 of the 6 groups had the bar present during the ITI, 3 did nor. During extinction half of each group received the dipper click, half did not. During extinction the SOC-NC groups were significantly more resistant to extinction than the other 100% and 50% groups, which did not differ sign~f~canrly. Results were discussed i n terms of a discrimination hypothesis of secondary reinforcement.