Immunohistochemistry is a very useful tool in the localization and functional characterization of specific proteins in cells and tissues. For an authentic interpretation of the results from the immunohistochemical analysis, it is necessary to carry out the process on the samples that would certainly give a positive result (positive control), and the samples that will certainly give a negative result (negative control). The positive control is particularly important in the case of negative immunohistochemical signal of the examined tissue. In the study of the role of neurotransmitter GABA (gamma-aminobutyric acid) in the regulation of secretion of mucus in endocervical secretory cells, an immunohistochemical examination of the presence of molecules of GABA signalling pathway in human cervical tissue was conducted. Unexpectedly, this analysis gave a negative result for GAD (Glutamate decarboxylase) and VGAT (Vesicular GABA transporter) in the cervix tissue. Due to the lack of positive controls, that result could not have been credibly interpreted. ----- The aim of this study was to get a positive signal for GAD and VGAT in the tissue where it’s known that it contains these molecules. For this purpose the selected tissues were brain, lung and testes of the mouse. It was necessary to adapt the procedure for immunohistochemical detection of GAD and VGAT in paraffin sections of tissue, since the research was carried out on paraffin sections of human tissue of the cervix. Positive immunohistochemical result showing GAD and VGAT in brain and testes tissues showed that this tissue may be used as positive controls for immunohistochemical analysis of the presence of these molecules in paraffin sections of tissue. Finally, immunohistochemical analysis of human cervical tissue showed a negative signal for GAD and VGAT in the tissue, while the GABA receptor signal was positive. With positive control established in this study and the corresponding negative control for the GABA receptor, the results of this experiment can be reliable.