Objectives. To measure the level of stem cell factor (SCF) in human seminal plasma to determine whether SCF may be useful in evaluating the ability to produce sperm and search the role of SCF in the testes.

Methods. We measured the level of SCF in seminal plasma obtained from 108 males, including idiopathic azoospermia due to germ cell aplasia (n = 10), oligospermia (n = 50), asthenospermia (n = 31), and normospermia (n = 17). The expression of SCF messenger ribonucleic acid in the human testis was evaluated by reverse transcriptase polymerase chain reaction (RT-PCR). The correlation between its level and clinical findings was also evaluated.

Results. RT-PCR showed a larger form that encoded the soluble protein and a smaller form that encoded the membrane-associated form of SCF in the human testis. The similar ratio of the larger form to the smaller one was observed both in the testis of normal and oligospermic men. The level of SCF is significantly correlated with the sperm count (r = 0.214; P <0.05).

Conclusions. The level of SCF in seminal plasma appeared to predict the ability to produce sperm. Thus, this factor may play an important role in spermatogenesis.