Although it is well known that the effect of temperature is important in the transformation of Leishmania promastigotes into amastigotes under axenic conditions, the contribution of this variable in the transformation of intracellular parasites is presently unknown. When J-774 murine cell line macrophages were infected with Leishrnania amazonensisat two different temperatures (24 and 33OC), intracellular parasites were observed at both temperatures. The resulting intracellular parasites were compared by morphological, immunological and structural criteria. The results indicate that while parasites produced at 33°C have characteristics similar to those previoulsy reported in the literature, infection of macrophages at lower temperatures resulted in intracellular parasites with no evidence of transformation into amastigotes. These results indicate that temperature is essential for the intracellular transformation of promastigotes into amastigotes.