To evaluate the relationship, both quantitative and qualitative, between the Ito cells and methotrexate (MTX) therapy Ito cells were studied by light microscopy in 1 mum toluidine blue stained sections and by electron microscopy in 24 pairs of Menghini needle biopsies before and after MTX therapy of 24 consenting patients with severe psoriasis. Light microscopy showed a statistically significant increase in pathological findings (P less than 0-05) and in the number of Ito cells and their size (P less than 0-0001) after MTX therapy. It was not possible to show a statistically significant correlation between the increase in the number of Ito cells and the cumulative dose of MTX. Ultrastructural analysis of Ito cells showed no marked difference from pre to post-MTX specimens. The fibrosis and cirrhosis seen after MTX therapy in some liver biopsies from psoriatics and the post-MTX increase in the number of Ito cells direct attention to the possible role of Ito cells as fibroblast precursors.