The effect of two concentrations of caffeine (1500 <FONT FACE="Symbol">m</FONT>g/ml and 2500 <FONT FACE="Symbol">m</FONT>g/ml) on mitotic indices of Drosophila prosaltans was analyzed in larval brain cells. Although the differences detected between treated and control cells were not significant, the percentages obtained suggest a possible effect of caffeine in slowing the process of cell division