The stability of chlorpyrifos methyl (Reldan) insecticide, Multicri I (FF) and/or their mixture -mixed with rats' diet were studied at intervals of time using thin layer chromatographic method. Results showed that no degradation or interference were found up to seven days after treatment, however, different degradations were found during the next experimental period (21 days). The biochemical studies showed that the compounds tested and/or their mixture had a great effect on different serum enzymes activities. Also the cytogenetic studies focused the chromosomal damages induced by Reldan, multicri I and their mixture which evaluated by determining the frequencies of different type of chromosomal aberrations in bone marrow cells. These aberrations were presentenced by chromatid breaks, chromosomal breaks (ring chromosome) and chromosomal fragments.