Abstract. Acid-labile sulfide measured by conventional gas dialysis and ion chromatography with electrochemical detection accounts for only a proportion of the total sulfide present in brain tissue after poisoning with NariS, an H2S precursor. Dithiothreitol (DTT) displaced additional measurable sulfide not detectable by the conventional techniques from NariS-poisoned brain tissue. Sulfide liberation by DTT was dose-dependent and maximal at higher DTI" concentration (10 and 30 mM) and was thought to represent non-acid labile sulfide. Dithiothreitol was also found to be significantly protective against H2S poisoning. Furthermore, in vitro inhibition by sulfide of monoamine oxidase (MAO) was reversed by DTT, thus suggesting a molecular mechanism consistent with known persulfide chemistry. Persulfide formation may thus underlie some aspects of hydrogen sulfide neurotoxicity. The rational development of antidotes for use in H2S poisoning may thus have to be centered on strategies concentrating on known thiol, disulfide and persulfide chemistry.