The presence of trichothecenes, such as T2 and DON, together in foods with Z and evidence that DON and Z may interact to enhance each other's toxicity prompted this study. The effects of these toxins on RNA, DNA, and protein synthesis (using radiolabeled amino acids, C-14 uridine and H-3 thymidine, respectively) on rat (8-10 wks old) spleen slices cultured for 90 min in KRP buffer, pH 7.4, at 37° was studied. Levels (n=6) were 0.0, 0.001, 0.01, and 0.1 µg/ml for T2; 0.1, 1.0, and 10.0 µg/ml for DON; and 0.4, 4.0, and 40 µg/ml for Z. For T2, minimum effect-level for inhibition of protein and DNA synthesis was 0.1 µg/ml (91 and 88%); for DON, minimum effect-level for inhibition of protein and DNA synthesis was 1.0 µg/ml (72 and 53%); and for Z, minimum effect level for inhibition of protein, DNA, and RNA synthesis was 40 µg/ml (72, 76, and 44%). RNA synthesis was stimulated by Z or DON at 1 µg/ml.There was no interaction between DON and Z, each at 1.0 µg/ml, for effects on macromolecular synthesis- the effects were essentially additive. In general, protein and DNA synthesis were the most sensitive parameters for all the toxins. T2 was by far the most potent--as in other test systems.