The efficiency of applying cell-free-extract and immobilization techniques in the bioconversion of 19-nortestosterone steroid into estrone and estradiol by Rhodococcus sp. DSM 92-344 was investigated. The utilization of cell-free-extracts significantly improved the productivity of estrone and estradiol and reduced the time of transformation as compared with intact cells. Ca alginate at a gel concentration of 2% (w/v) was most suitable for entrapping Rhodococcus cells to perform the most efficient substrate conversion and estrone formation. Maximum estrone yields were obtained after 48 and 60 h when shaken immobilized cells were used. The highest bioconversion efficiency of substrate to estrone was attained after 48 h by using an air-lift column. Repeated use of entrapped cells (more than four cycles) in the fluidized-bed bioreactor was accompanied by lowered dehydrogenase activity and hence estrone and estradiol yields.