Nucleolar organiser regions (NORs) are loops of DNA situated on the short arms of acrocentric chromosomes 13, 14, 15, 21, and 22. They can be demonstrated in formalin-fixed paraffin-embedded sections by a one step silver technique; the resultant black structures are called AgNORs. The technique was used in 71 patients with cutaneous malignant lymphomas (CML) and 9 cutaneous pseudolymphomas (CPL). AgNORs in 200 nuclei were scored and the means, standard deviation and standard error of the means calculated. Counts were as follows: mycosis fungoides (MF) I (premycotic stage) 1.17 +/- 0.09, SEM = 0.01; MF II (infiltrating stage) 1.17 +/- 0.01, SEM = 0.02; MF III (tumor stage) 3.55 +/- 0.87, SEM = 0.43: cutaneous peripheral T cell lymphomas other than MF and Sezary's syndrome (SS) (CPTL) 2.55 +/- 1.11, SEM = 0.35; SS 1.52; cutaneous B cell lymphomas (CBCL) 2.18 +/- 0.18, SEM = 0.06; CPL 1.17 +/- 0.1, SEM = 0.03. There was a significant difference between counts for CML (MF III, CPTL, CBCL and SS) and CPL. Significant difference was also noted between scores for MF III and CBCL, and especially counts between tumor stage (MF III and CPTL) and pretumor stage (MF I and MF II) of cutaneous peripheral T cell lymphomas. Although the AgNOR technique is in the stage of research, it proves to be helpful in differentiating CML and CPL other than separating MF I and MF II from CPL.