The area of lymphocyte nucleoli (ALN) is a recently imagined method (Micu et al., 1978) which can detect cytochemically the microscopically visible surface of nucleolar RNA, measurable in mu2. The normal ALN value in peripheral blood is 84.4 +/- 9.2 mu2. Using in vitro cultures of PHA-stimulated lymphocytes obtained from 106 patients with various internal diseases, the authors could demonstrate a relationship between the rate of the lymphocytic RNA biosynthesis and the ALN variations, namely that an RNA hyper- or hyposynthesis is accompanied by an increase or a decrease, respectively, of the ALN.