Mosquito larvae soluble fractions obtained by molecular exclusion chromatography altered the mitotic rate of several epithelial cell populations in hepatectomised mice, as well as the proliferation of human mononuclear cells (MNC), stimulating or inhibiting them depending on the fraction and dose applied. The effect was also thermolabile, suggesting a proteic nature of the compounds involved. Analysis of cell viability after culture indicated that the extract did not have lethal toxic effects. One fraction with a molecular weight ranging between 12–80kDa caused only an inhibitory effect. In the present study, we performed further characterisation of this fraction by assaying the effect of new fractions obtained from this one, by the use of a column with a lower molecular weight exclusion range. Assays were performed on the proliferation of adult human MNCs. Our results showed that two out of four of the sub‐fractions analysed, with a MW of about 70 and 17kDa, caused a dose‐dependent response, either inhibiting or stimulating MNC proliferation respectively.