The RNA probe was in vitro transcribed with the recombinant of the Y-chromosome specific deoxyribonucleic acid (DNA) sequence and transcription-vector Bluescript SK M13+. The preparation of the RNA probe is not difficult, but it does require a subcloning procedure which is unnecessary in the preparation of the DNA probe. The results indicate the superiority of the RNA probe over the previously studied DNA probe. The RNA probe has a high hybridization efficiency which increases the sensitivity of the test and shortens the period of time necessary for obtaining the resulting stains. 2 figures, 7 references. (Author abstract modified)