Recently, a 40% reduction in the total of oxytocin immunoreactive neurons of the paraventricular nucleus of the hypothalamus in AIDS patients was reported. In the present study, we determined whether this decrease is associated with a diminished amount of oxytocin mRNA. We used in situ hybridization combined with densitometric image analysis for the quantitative assessment of oxytocin gene expression in the paraventricular nucleus of a group of AIDS patients (n=10) and a carefully matched control group (n=8). We found no significant difference (P=0.08) in the amount of oxytocin mRNA per total paraventricular nucleus between the two groups. In addition, no significant differences were found in the part of the volume of the paraventricular nucleus that was occupied by hybridized cells (P=0.12) or in the mean signal density (P=0.08). The findings do not support the hypothesis that the extensive decrease in oxytocin immunoreactive neurons of the paraventricular nucleus in AIDS is associated with a decrease in total oxytocin mRNA content in this nucleus. The data are compatible with the suggestion that in AIDS the biosynthesis of oxytocin is changed in an unknown way at the (post)transcriptional level.