PURPOSE: To obtain a diagnostic reagent for male sterility by using a hydrophobic bead and ionophor as requisites.

CONSTITUTION: A hydrophobic bead is a bead of which a free radical in a structural formula is highly hydrophobic, and it is the bead of phenylagarose or phenylcephalose CL-4B or CL-6B. For a sperm which causes an acrosomal reaction, these substances act as if they were an ovule, and the sperm senses the chemical substances forming the bead and couples thereto. As for ionophor, gramicidin or ionomycin is preferable and these induce biological reaction for the sperm. In the case when non-coupling of the sperm to the hydrophobic bead is observed in the field of medical treatment, it can be diagnosed as an important factor of male sterility. When the coupling is observed in the case of stockbreeding, the sperm is regarded as excellent for breeding.