- The presence of germ cells in the semen of azoospermic, cryptozoospermic and severe oligozoospermic patients: stringent flow cytometric analysis and correlations with hormonal status. Yeung, C.H., Beiglböck-Karau, L., Tüttelmann, F., Nieschlag, E. Clin. Endocrinol. (Oxf) (2007)