1 The effects of pretreatment of guinea-pigs with 6-hydroxydopamine (6-OHDA) on the release of [(3)H]-noradrenaline and [(3)H]-adenine nucleotide following electrical field, nicotine and perivascular nerve stimulation of guinea-pig taenia caecum were studied.2 High frequency electrical field stimulation (15,30 Hz) released both [(3)H]-noradrenaline and [(3)H]-adenine nucleotide but low frequency (0.5, 5 Hz) stimulation, producing comparable muscle relaxation led only to [(3)H]-noradrenaline release.3 6-OHDA (50-200 mg/kg) pretreatment inhibited the muscle relaxation and [(3)H]-noradrenaline release with electrical stimulation or with nicotine in isolated taenia but did not affect the release of [(3)H]-nucleotide.4 A low dose of 6-OHDA (50 mg/kg), completely inhibited the muscle relaxation and [(3)H]-noradrenaline release elicited by perivascular nerve stimulation.5 Both tissue noradrenaline content and [(3)H]-noradrenaline uptake were decreased to the same extent by low as well as high doses of 6-OHDA: noradrenaline content was reduced to 20% and uptake to 30% of the control value.6 Catecholamine fluorescence disappeared from tissue layers of the taenia after treatment with a high dose of 6-OHDA.7 In these experiments the inhibitory action of electrical stimulation and nicotine on the taenia can be correlated better with noradrenaline than with nucleotide release.