AbstractThe effects of tartar emetic and bilharcid, two antimonial antibilharzial drugs, on the chromosomes of laboratory rats are studied. The drugs were administered intraperitoneally in three doses—clinical, intermediate, and maximum tolerated — both acutely (6, 24, and 48 hours) and subacutely. The two drugs produced the same types of chromosomal aberrations with tartar emetic, inducing a higher rate of incidence. No significant differences in the number of cells with chromosomal aberrations were generally observed among the 6, 24, and 48 hours of the acute treatment with both tartar emetic and bilharcid. The dose‐response relationship was examined for both the acute and the subacute treatments. Whereas the acute treatment of tartar emetic showed a dose‐dependent linear increase in the number of cells with chromosomal aberrations, the subacute treatment of tartar emetic and the acute and subacute treatments of bilharcid displayed their maximum effects at an intermedia