The study was conducted to evaluate some immunological (total and absolute counts of leucocytes), cytogenetic (mitotic index of bone marrow cells, micronucleus formation in bone marrow cells and sperm-head abnormalities), biochemical (glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), alkaline phosphatase (ALP) and total bilirubin in serum) and histopathological (liver) effects of oregano (Origanum vulgare L.) fresh leaf extracts (methanol and hexane), and their effects on carbon tetrachloride (CCl4)-induced acute hepatic injury in albino male mice. Therefore, such evaluations were carried out through two stages. In stage I, three doses (32, 64 or 96 mg/kg) of oregano extracts and a single dose (3.2 mg/kg) of CCl4 were investigated. The tested materials were injected intraperitoneally as a single dose (0.1 ml) per a day and for 7 days, and then the mice were sacrificed on day 8 for laboratory assessments. In the case of CCl4, it was injected subcutaneously as a single dose (0.1 ml) for one a day, and then the mice were sacrificed in the second day. In stage II, interactions between the three doses of both extracts and CCl4 were carried out. In such interactions, the animals were given CCl4 on day one, while the plant extract was given in day 2 till day 7 (single dose/day), and then animals were sacrificed in day 8 for laboratory assessments. Chemical detections of oregano extracts revealed that the plant is rich in several compounds. In methanol extract, flavonoids, coumarins, tannins and phenolic compounds were detected, while hexane extract was positive for terpens, steroids, tannins and volatile oils. The results revealed that CCl4-treated animals showed significant decreased counts of total and absolute counts of leucocytes, and such observations suggest the CCl4 is an immune suppressive agent. Furthermore, significant increased percentages of induced micronucleus formation and sperm head abnormalities and a significant decreased mitotic activity of bone marrow cells in the treated mice were also observed, therefore CCl4 can be considered as a mutagenic agent. In contrast, methanol and hexane extracts of oregano were significantly effective in enhancing the values of the investigated parameters, especially the mitotic index, which showed a significant increase, and the spontaneous micronucleus formation and sperm head abnormalities, which showed a significant decrease. However these effects were dependent on dose and type of extract. The results of interactions between CCl4 and both oregano extracts confirmed the forthcoming effect of the plant, and the two extracts were significantly effective in modulating the immune suppressive and mutagenic effects of CCl4, although the effects were also subjected to the dose, type of extract and the parameter of evaluation. Liver sections of animals treated with CCl4 showed marked degenerative areas and necrosis of hepatocytes around the central vein. Moreover, significant increased serum levels of GOT, GPT, ALP and total bilirubin were observed in the animals, and such findings reflected induced hepatic damages. In contrast, biochemical parameters confirmed the hepatoprotective effect of oregano extracts through decreasing or normalizing the serum level of these enzymes and repairing the induced cellular damage of liver. However, a histopathological examination of liver sections was still showing some of the CCl4-induced hepatic histological damages.