Contamination of food and feeds by mycotoxins is a major problem of human and animals health concern which is also extremely detrimental to economy. Mycotoxins producing moulds may produce a diversity of toxins such as aflatoxins, ochratoxins, trichothecenes, zearalenone, fumonisins, tremorgenic toxins and ergot alkaloids. Although toxicological, environmental and epidemiological studies have addressed the problem of these toxins one by one, more than one mycotoxin are found usually in the same contaminated commodities. That rises the incommensurable problem of multi-toxicosis in which the respective metabolites are also involved. These mycotoxins bear potential toxicity leading to acute and chronic effects in humans and animals, depending on species. The mechanisms that lead to toxic effects, such as immune toxicity, and carcinogenicity are complexe. The risk assessment for humans potentially exposed to multi-mycotoxins suffers very much from the lack of adequate food consumption data. Furthermore, for a given mycotoxin synergism and antagonism with other mycotoxins found in the same food commodities are not taken into account. The case of combination of ochratoxin A (OTA) and fumonisin B1 (FB1) has been addressed in the present paper with the purpose of predicting the in vivo toxicity using a simple in vitro test, i.e. neutral red uptake, in three different cell-lines, C6 glioma cells, Caco-2 cells and Vero cells. Using the equation of [ATLA 27 (1999) 957], in vivo toxicity (LD50) is in adequation with the in vitro data, (IC50 values) for both toxins as well as for the combination of 10 microM OTA and variable concentrations of FB1 (10-50 microM). A synergistic effect is prouved in vitro that is in line with some in vivo data from the literature. Such simple in vitro test may thus help predicting in vivo toxicity of combinations of mycotoxins naturally occurring in foodstuffs.