Dimethoate, bromophos, naled or trichlorophon were applied i.p. or p.o. to rats in 3 doses each differing by the factor 10. In the urine of 24 h gas chromatographic determination of dimethylphosphate (DM), O.O-dimethylthiophosphate (TP), and/or O.O-dimethyldithiophosphate (DT) were carried out. After i.p. application of dimethoate the excretion rate of DT calculated from the dates found with the lowest dosage differed significantly from those found with the two other doses (t-test; p = 0.01). The excretion rates of DM and TP, in the same way, or those of DM, TP, and DT after oral intake of dimethoate did not show any significant differences. The excretion rates of TP after bromophos and of DM after naled or trichlorophon did not differ significantly after the same way of application. The findings make evident that under the given test conditions the excretion rate of DM, TP, or DT is practically independent on the dose.