Abstract:Nociceptive stimulation has been performed in rats with a technique which should allow us to study different pain projection levels within the central nervous system. Three different types of thresholds were studied by electrical stimulation and the stimulus responses were qualitatively and quantitatively divided into a) motor response b) vocalisation and c) vocalisation after‐discharge. Caffeine and theophylline were able to decrease the thresholds for motor response and vocalisation in a dose‐dependent manner. Both drugs were also able to reduce the thresholds for vocalisation after‐discharge. However, caffeine reduced this response to about 50‐60% of the normal, but not in a dose‐dependent manner, which is contrary to theophylline which, in a dose of 100 mg/kg, decreased the threshold to as little as 20 per cent of the normal. In general, maximum effects were obtained 30 minutes after administration and theophylline produced more long‐lasting effects th