Objective To study the application of census method in estimating the size of population of commercial sex workers(CSW),and estimatie the size of population in CSW in a city.Methods Drawing the map of the place which applied sex service,collect the number of CSW which the manager of place report.Sample 20% place of total,check the amount of all CSW,then adjust the sum of managers reported according the number of investigator checked and the number of manager reported to estimating the size of population in CSW in the city.Results The result of census in estimating the CSW in the city was 18 702.Conclusions It is simple and direct to estimate the size of population in CSW by applying the census method.The result is reliable,but the method need the investigators know very well the palce applied sex service in the area.

Objective To study the application of Capture-Recapture method in estimating the size of population of injecting drug users (IDUs), and estimate the size of population in IDUs in a city using the data of detoxification center. Methods Capture-Recapture method was applied to estimating the size of population in IDUs in the city based on the data of detoxification center. Results The result of Capture-Recapture in estimating the IDUs in the city was 13 017. Conclusions It is economic and feasible to estimate the size of population in IDUs by applying the Capture-Recapture method. The result is reliable and the method is suitable in districts where health resources are limited.