Modern and effective biomedical research needs new and effective methods. Use of 96 well-microtiter lates allows the performance of many experiments and samples under the same conditions. Methods to determine cell numbers in 96 well-microtiter plates are all endpoint methods. Methods for determination of cell numbers such as measuring the incorporation of radioactive nucleides like thymidine, MTT, XTT, MTS, lactate dehydrogenase, acid phosphatase, etc. allow only one determination per plate and the cells are lost. Usually such assays are performed according to concentration dependance. Other parameters and cell growth dynamics remained unrevealed. To reveal cell growth dynamics multiple assays should be performed. Such experiment approach would be expencive and time consuming so it is rarely performed. To fill this gap IAM and SLT Labinstruments developed GCSS (General Cell Screening System). GCSS is a powerful hardware and software system that enables continuous monitoring of the cell growth without any treatment or stain. The method is based on a high resolution turbidity measurement (700 nm) performed directly in the 96 well cell culture plate. The system consists of the GCSS-reader and 8 channel photometer, (the beam has the form of a narrow rectangle), the GCSS- plate with a new form of the wells, an Apple Macintosh computer and the GCSS-Software. We chose classic bone marrow colony count assay, which is tipical assay scored after seven days of incubation and based on one measurement only. GCSS allowed us, to seed bone marrow cells in microtiter plates in medium with different concentrations of haemopoietic growth factors and performed multiple measurements. In this experiment we observed bone marrow cell growth derived from interferon alpha treated mice and compare the cell growth from placebo treated mice. Classical bone marrow assay which has based on one measurement only allowed scientists to confirm suppressive nature of interferon alpha on bone marrow cells in vivo. Multiple measurements with GCSS allowed us to collect cell growth data during seven days of incubation which could not be seen in colony count assay. The collected data with GCSS could not confirm suppressive nature of interferon alpha but revealed that interferon alpha is bone marrow cells activator in vivo. We expect that GCSS will have important influence in new biomedical research and in corrections of established assays too.