Reinforcement omission effects (ROEs) have beeninterpreted as behavioral transient facilitation after nonreinforcement inducedby primary frustration, and/or behavioral transient inhibition afterreinforcement induced by demotivation or temporal control. According to frustrationtheory, the size of the ROEs should depend directly on the reinforcementmagnitude: the behavioral facilitation after thereinforcement omission of larger magnitude should be greater than that observedafter the reinforcement omission of smaller magnitude. However, studiesinvolving operant paradigms have presenteddifficulty to demonstrate this relationship. Thus, the present study aimed toclarify the relationship between reinforcement magnitude and ROEsmanipulating the magnitude linked to discriminative stimuli in a partialreinforcement fixed interval schedule. Rats were trained on a fixed-interval 12 s with limitedhold 6 s signaled schedule in which correct responses were always followed byone of two reinforcement magnitudes (0.5 and 0.05 ml of a 0.15% saccharinsolution). After acquisition of stable performance, the training was changedfrom 100% to 50% reinforcement schedules. The results showed that responserates were higher after omission than after reinforcement delivery. Besides,results showed that response rates were highest after the reinforcementomission of larger magnitude than of smaller magnitude. However, thefindings did not support the hypothesis that the reinforcement omission of largemagnitude induces greater behavioral facilitation than the reinforcementomission of smaller magnitude. The data were interpreted in terms of ROEsmultiple process behavioral facilitation after nonreinforcement and behavioraltransient inhibition after reinforcement.