FIELD : medicine.SUBSTANCE : group of inventions relates to medicine and relates to a method for increasing specific pinch of a neurotoxic polypeptide by cells, involving incubation with a neurotoxic polypeptide of cells sensitive to intoxication by neurotoxin, over time and under conditions that allow the neurotoxic polypeptide to exhibit its biological activity, wherein the incubation comprises at least two of the following steps : (I) K+-mediated cells depolarization, (II) reduced exposure time to neurotoxic polypeptide of at least 24?hours and less than 96?hours, and/or (III) shaking of cells during exposure to the neurotoxic polypeptide, resulting in higher specific pinch of the neurotoxic polypeptide by mentioned cells, moreover, the specific pinch of the neurotoxic polypeptide into the cell was increased by at least 1.5 times compared with the method using cell culture conditions that do not include (I), (II) and/or (III). Group of inventions also relates to a method for direct determination of biological activity of a neurotoxic polypeptide in cells.EFFECT : group of inventions provides higher specific pinch of the neurotoxic peptide in cells.15 cl, 2 ex, 1 dwg