Alternaria tenuissima is commonly isolated from wheat in Argentina. The objective of this study was to examine the effects of temperature (15-34 degrees C) and water activity (0.98, 0.95 a(w)) on growth and temporal altertoxin II (ALTX-II) production by two strains over 14-21 days on a milled wheat agar. It was shown that growth occurred over the whole temperature range tested and was optimum at 25-30 degrees C and 0.98 a(w) and 30 degrees C at 0.95 a(w) The incubation time did not show any significant effect on ALTX-II accumulation. The optimum conditions for ALTX-II production were 0.98 a(w), and 30 degrees C for both strains. The strains also accumulated significant amounts of this toxin at 34 degrees C. This is the first study to evaluate the ecology of growth and production of ALTX-II by strains of A. tenuissima.