The applicability of a simple noncompartmental organ clearance approach was extended to evaluate the effect of change in blood flow (Q) on hemodialysis clearance (CL) using patient data reported in the literature. Hemodialysis blood or plasma clearance data of vitamin B12, urea, creatinine and uric acid were fitted into the equation, CL = HQ/(Q + H), where H is the apparent intrinsic hemodialysis clearance for total (bound and unbound) compound. The Q values varied up to 16-fold. The extraction ratios ranged from about 0.4 to 1.0 (indicating existence of marked concentration gradient) and 0.1 to 0.6 for urea and vitamin B12, respectively. The H only serves as an "operator" in a given system, and the H value per unit length of the dialyzer coil can be shown to increase markedly with the length of coil, which is different from the basic assumption in the well-stirred model. For vitamin B12 the present clearance approach appears to be slightly superior to the "parallel-tube model".