Today, 2,4-dichlorophenoxyacetic acid (2,4-D) is a widely used herbicide and is has been the subject of many studies related to carcinogenicity, chronic toxicity, genetic toxicity and reproductive toxicity. In this study,the effects on rats exposed to the acidic form of 2,4-D were evaluated with histopathological and plasmatic parameters. Rats were orally exposed to 25 and 50 ppm of 2,4-D in drinking water daily, and 50 and 100 ppm dietary feed for a period of 45 days. At the end of the study, serum glutamic oxaloacetic transaminase (GOT), serum glutamic pyruvic transaminase (GPT) and creatine phosphokinase (CPK) values were examined from rat blood samples, and also tissue samples from rat brain, heart, lungs, liver, kidney, thymus and testis were histopathologically examined. Extensive parenchymal degeneration in the liver, mid-grade parenchymal degeneration in kidneys, and cortical hyperplasia in the thymus were observed in the group exposed to a maximum dosage (100 ppm) and, in one of the rats, lymphoidal cell increase in the cortex and significant follicle formation with epithelial cells creating starry sky patterns between the lymphocytes were observed histopathologically. Rats with liver injuries were also observed to have increased serum GOT values. Consequently, our findings supported that 2,4-D is a toxic agent, possibly causing lymphoid tumors.