A description of an automatic micrometric apparatus constructed by the authors. The apparatus is served by an electric motor and an interval time disconnecting swith is used. Calibration of the apparatus showed a precision of dosage, determined by the use of the variability coefficient WZ=0,6-6,5%. Calibration was made by weight using hydrargyrum and colorimetric method to determine the dispersion of the size of the single drops. Crystal violet was used as the stain. Biological testing conducted on females of the house fly (Musca domestica L.) cultivated under laboratory conditions showed in the course of the determination LD50 - gamma HCH the accuracy WZ=9,7%.