Abstract: A method and apparatus for investigating various parameters of biofluids, such as blood, particularly protein and cellular concentrations and cellular volume utilises the application of at least two a.c. frequencies, preferably simultaneously, in the range 0.1 to 60 MHz to a sample of the fluid and receiving and resolving the frequencies after passage through the fluid. The received frequencies are processed to derive corresponding d.c. voltage amplitudes which are mathematically processed to provide a numeric output correlating with a parameter under investigation, A new parameter named Instant Sedimentation Rate (ISR) is disclosed.