A method for performing a photopheresis procedure is provided comprising collecting MNCs in a suspension comprising RBCs and plasma and lysing the red blood cells in the solution, preferably by combining the suspension with a solution to cause lysis. In one example, the solution for causing lysis of the red blood cells comprises ammonium chloride, and the suspension including the ammonium chloride is incubated to cause lysing. After lysing, the suspension may be washed to remove plasma and hemoglobin freed by the lysis of the red blood cells, and an ultraviolet light activated substance is added to the suspension. The suspension is then irradiated with ultraviolet light.