Abstract: A method of performing biorheological measurements on a suspension (4) of cells by causing some of the cells to pass through one or more microsize tunnels (3) in a solid medium (1, 2) under a pressure difference between the tunnel ends and monitoring (6) their passage through the tunnel or tunnels, characterized in that the pressure difference is monitored to produce a signal which is recorded or is utilized to provide feedback to regulate the biorheological measurements. Apparatus for performing this method may have such a pressure feedback control, or may have tunnels with at least partly transparent walls for transmitting optical information to a detector for the biorheological measurements.