The aim of this study was to identify the pharmaceutical substances in the waters of the river Volturno in Campania and to identify the genetic alterations that they induce in fish. These vertebrates, living in water, are particularly sensitive to polluting substances dissolved in their water that interact with DNA leading to the formation of additions or breaks, as well as to the loss or chemical modifications of the bases, because they can conserve and concentrate the substances discharged into their natural habitat. A preventive chemical analysis was carried out on the waters of the river Volturno. The results showed the presence of various drugs, among which Carbamazepine, a known antiepileptic and Diclofenac, a non-steroid anti-inflammatory agent. The genotoxicity of these two compounds was evaluated in 155 individuals of Danio rerio using the Comet Test, the Diffusion Assay and RAPD-PCR. The alkaline version of the Comet Test was used for the erythrocytes of the zebrafish to evaluate the presence of DNA breaks of a single strand. Furthermore, the Diffusion Assay was used to estimate the number of apoptotic cells. The specimens were treated with Carbamazepine and Diclofenac at the same average concentrations found in the river Volturno and were killed after three, seven and fifteen days. The results of the Comet Test showed a statistically significant loss of DNA integrity after only three days of exposure to the drugs. Also the percentage of apoptotic cells reached its maximum values after three days of exposure to Carbamazepine and after one week to Diclofenac. By RAPD-PCR the genotoxicity was evaluated at the molecular level. The amplification products from the individuals exposed to the same concentrations of the environmental pollutants showed significant changes in their electrophoretic pattern with respect to the negative controls. The results of all three tests clearly show the genotoxicity of the compounds analyzed.