The attention of researchers was focused on the study of the causes of regular refusals to receive services under HIV/AIDS programs, as well as on determining the mechanisms to attract and retain customers among IDU, FSW and MSM in the harm reduction projects. The study had a specific feature in its approach to sampling. Among NGO clients invited to participate in a survey, i.e. IDU, FSW, MSM, were both regular and irregular recipients of NGO. And the frequency to use NGO services was determined in accordance with the customer database of harm reduction programs SyrEx, and by the self-determination of the respondents. Such an approach allowed to compare the answers of the resondent groups, and to analyze the availability of the statistical relationship between the list of health and social services and the regularity of their receipt; between the motives for receiving services under the harm reduction project by representatives of specific vulnerable groups and the regularity of receving such services; between the frequency of sharing/receiving syringes by IDU clients and the safe injecting.