'-T-cell receptor (TCR) clonality is important for the diagnosis of mycosis fungoides (MF). Routine clonality analysis is performed using a polymerase chain reaction (PCR) TCR-γ assay; yet with this method 10%-50% of T-cell lymphomas escape detection. TCR-β gene rearrangement is an additional assay. Data about its efficacy is controversial.- To evaluate the role of TCR-β assay in the diagnosis of early MF.A retrospective study of 61 skin biopsies, 20 from MF patients, 30 from patients suspected to have early MF, and 11 from patients with chronic inflammatory skin disease.- Monoclonality was detected in 16/20 (80%) MF cases; 15 (75%) with TCR-β and 12 (60%) with TCR-γ assay. Of the 30 suspected early MF cases, 14 demonstrated monoclonality with TCR-β and only 5/14 with TCR-γ assay. None of the chronic inflammatory condition samples showed monoclonality. Therefore, TCR-β clonality assay was more sensitive in early MF than TCR-γ (83% vs. 43%, P=0.002).- A retrospective, relatively small study.- TCR-β demonstrated a higher sensitivity rate compared with TCR-γ in early-stage MF. The combined use of the TCR-β and TCR-γ clonality tests can significantly improve the diagnosis rate of early-stage MF.