The present work is an attempt to confirm the sub-chronic adverse effects of parathion, either in its technical (99 % ai) or formulated form (40 % EC) on blood picture, liver function, cholinesterase activity and cytochrome-C- system in male albino rat (Rattus norvegicus). Animals received a sub-lethal dose (1/20 LD50) of technical or formulated parathion either orally or dermally at 2-day intervals for 90 days on the light of the protocol proposed by EPA (1979). Results revealed that parathion insecticide caused signficant ohgocythemia accompanied by severe haemoglobinaemia resulting in significant rise in total bilirubin level in plasma which confirm its haemolytic effect. The hepatic toxicity of parathion was evident through the hyper-activation of transaminases indicating a hepatic disorder and/or damage. On the other hand, a significant decline in the plasma cholinesterase activity was recorded confirming the neurotoxicity of this organophosphorus insecticide. Furthermore, the respiratory toxicity of parathion was ascertained. The treatment caused 6-23% fall in the cytochrome-C content of different tissues showing a destructive effect to mitochondria. Contrarily, cytochrome-C oxidase and succinate cytochrome Creductase activity was enhanced which appeared to be due to the increase in the dehydrogenases activity rather than the stimulation of respiratory system. The present results also indicated that parathion revealed haematohepato, respiratory as well' as neuro-toxicity even when administered at sub-lethal doses. In addition, the formulated form exhibited higher toxicity than the technical one indicating that the additives must have possessed an inducing particularly when given orally. This leads to the confirmation that the final toxic classification of pesticides must be based on both the technical and formulated forms.