Toxicities expressed as LD50 values of 2-dialkylaminoalkyl-(dialkylamido)-fluorophosphates for rats and mice (i.m. administration) were determined. Rats were more sensitive to these compounds than mice: LD50 values varied from 17 (rats) to 1222 (mice) ^g/kg. LD50 values at different routes of administration (i.v., i.m., s.c., p.o. and p.c.) for one derivative of this group, 2-dimethylaminoethyl-(dimethyIamido)- fluorophosphate, were determined. Depending on the route of administration, LD50 values varied from 11 (i.v.) to 190 (p.o.) pg/V.g for rats and from 27.6 (i.v.) to 222 (p o.)/rg/kg for mice, respectively. Percutaneous toxicity in rats only (LD50 = 1366//g/kg) was determined.