Toxicological evaluation of two recently reported treatment protocols for cyanide--SN (sodium nitrite) + DMAP (4-dimethylaminophenol) and SN + HA (hydroxylamine)--was carried out in male rats. Both treatments produced transient hyperammonaemia and decreased mean arterial pressure. Heart rate decreased and respiratory rate increased, but these changes reached the level of significance only after SN + HA. Histopathological lesions in lung, liver (SN+HA) and kidney (SN+DMAP) were predominantly in the vicinity of blood vessels. The results indicate toxic effects in both treatment groups at a dose known to induce methaemoglobin concentration to the level of antidotal efficiency in cyanide intoxication.