Methotrexate treatment for psoriasis is known to cause hepatic fibrosis in some patients, which might progress to cirrhosis. The fine, radiating, fibrous septa developing in this setting have a distribution that is reminiscent of the location of the canals of Hering (coH). To assess the possibility of fibrous obliteration of the coH in patients receiving methotrexate, we developed a staining technique by combining an immunohistochemical stain for cytokeratin 7 with a modified Masson trichrome. Sixteen biopsy specimens from 7 patients were evaluated. The biopsies had a variety of histologic changes, including steatosis, anisonucleosis, multinucleation, chronic inflammation, bile duct damage, and ductular reaction. Fibrosis was present in 13 biopsy specimens (81%) and was mild in 7, moderate in 3, and severe in 3 specimens. Compared with normal (control) liver specimens, biopsy specimensfrom patients receiving methotrexate had decreased numbers of coH (1.9 +/- 0.8 vs 5.2 +/- 1.7; P < .025). In specimens with moderate or severe fibrosis, fibrous septa sometimes extended along the coH. These findings suggest that scarring of the coH might be a consequence of the toxic effects of methotrexate.