Theoretical analysis of solute transfer in a dialyzer with ideal periodic flow patterns provides a quantitative basis of evaluating designs and interpreting data. For constant volumetric flow rate of blood in each half cycle, two mass transfer models have been developed: one with fixed thickness of the blood film and changing transfer area and another with changing thickness and fixed transfer area. Fractional solute removal is calculated for membrane-Sherwood number ranging from 0.01 to infinity and dimensionless cycle time from 0.01 to 70. The theoretical efficiency of the second model is about twice that of the first, and within 20% of that of a flow-through parallel plate dialyzer with the same blood film thickness and membrane area, In-vitro experiments of creatinine transfer agree with the first model within experimental accuracy.