ABSTRACT Ochratoxin A (OTA) and citrinin (CTN) are two mycotoxins, quite common contaminants, that can occur jointly in a wide range of food commodities. Both mycotoxins have several toxic effects but both share a significant nephrotoxic potential since OTA and CTN were reported to be responsible for naturally occurring human and animal kidney diseases. Considering the concomitant production of OTA and CTN, it is very likely that humans and animals are always exposed to the mixture rather than to individual compounds. Therefore, the aim of the present study was to investigate, using kidney cell culture (Vero cells), whether cytotoxicity and essentially oxidative cell damage (a key determinant of renal diseases) are enhanced by combination of both mycotoxins as compared to their effect separately. To this end, we have assessed their effects individually or combined on cell proliferation using three different cell viability assays (MTT, Trypan Blue, and Neutral Red). In addition, the role of oxidative stress was investigated by measuring the malondialdehyde (MDA) level and the expression of the heat shock protein Hsp 70. Our results clearly showed that cultured renal cells respond to OTA and CTN exposure by a moderate and weak inhibition of cell proliferation and induction of oxidative stress, respectively. However, when combined, they exert a significant increase in inhibition of cell viability as well as the induction of MDA level and Hsp 70 expression. OTA and CTN combination effects are clearly of synergistic nature. The enhanced induction of oxidative stress observed with OTA and CTN simultaneously could be relevant to explain the molecular basis of the renal diseases induced by these mycotoxins.