Use of aniline blue to assess chromatin condensation in morphologically normal spermatozoa in normal and infertile men.

Chromatin condensation is vital for the function of the spermatozoon as the motile carrier of the paternal genome. The degree of condensation can be shown with the aid of acidic aniline blue staining, which is able to discriminate between lysine-rich histones and arginine- and cysteine-rich protamines. Using this technique and employing the Düsseldorf classification of sperm morphology in cases of disturbance of spermatogenesis, it was demonstrated that chromatin condensation is impaired not only in malformed but also in morphologically normal spermatozoa. Among morphologically normal spermatozoa, the percentages of spermatozoa with chromatin condensation disturbances increase in patients with different patterns of sperm malformation, if compared with patients with normozoospermia.