A common feature in responding to chloramphenicol treatment for pea and wheat seedlings was the substantial increases in the rates of cyanide-resistant respiration. However, they were very different in many other aspects. Whole pea leaves appeared yellowish 3 or more days after chloramphenicol treatment. The chlorophyll content decreased by 30% after 9-10 days. In wheat seedlings, chloramphenicol treatment resulted in a complete loss of chlorophyll and formation of white tissues in the base of their leaves. The top region of leaves was still green. The un-inhibited rates of respiration decreased in pea, but increased in wheat mitochondria oxidising NADH. There was an approximately 5-fold increase in the activity of externally facing NADH dehydrogenase in wheat, but not in pea mitochondria. Western blot analysis showed that there were two additional bands of lower molecular weight alternative oxidases (32-33 kDa) in chloramphenicol-treated wheat leaf mitochondria, but there was no increase in alternative oxidase proteins in chloramphenicol-treated pea leaf and root mitochondria. Wheat seedlings responded to chlorarnphenicol treatment presumably by increasing the rate of glycolysis, while pea seedlings may have a different mechanism.