Some representatives of 1,3-bis-(5-ammoniopentyl)uracil dibromides with the anticholinesterase type of activity are classified as highly/moderately toxic in mice and as slightly toxic/practically nontoxic in daphnia. Under the conditions of functional testing (treadmill running test in mice, i.p.), compounds with less bulky substituents (H, F, Br, CH3, CN, NO2, and CH3O groups) at positions 5 and 6 of the uracil cycle are more effective and safer than proserine and BW284c51: (a) they induce the development of a clearly pronounced myorelaxant effect lasting over not less than one day (ED50 = 0.03 – 0.11 µM/kg), (b) the ratio LD50/ED50 is below 76.67. An increase in length of the aliphatic radical in position 5 of the uracil cycle leads to a gradual increase in the toxicity with respect to daphnia, while the toxicity with respect to mice exhibits a decrease.