D. Manoch, S. Kunathikom, T. Thaweechaithaworn, P. Phophong, and P. Laokirkkiat, “Hypoosmotic Swelling Test of Sperm Supplemented with Pentoxifylline after Preparation by Two-layer Percoll Gradient Method”, Siriraj Med J, vol. 56, no. 4, pp. 186–190, Apr. 2004.