Abstract: An apparatus and method for real-time measurement of an effect of different concentrations of a test compound or series of test compounds on living cells, in which a flow of cell suspension is combined with a flow of the test compound and a cellular response of the living cells is repeatedly measured by a detector along a length of a detection zone where the cell suspension-test compound mixture is situated. The apparatus may be used in automated screening of libraries of compounds, and is capable of real-time variation of concentrations of test compounds and generation of three-dimensional dose/response/time profiles within a short timespan.