Cyclosporin A (CsA), a relatively new drug, was previously used in a series of studies on experimental trichinosis. This work was conducted to study the histopathological changes of CsA treatment at different time intervals from T. spiralis infection in mice. The work included study of the effect of the drug on the larvae treated either in vivo or in vitro. The drug was most effective when it was administered on the same day of infection, then when given one week before. The effect was evidenced by diminution both in the number of larvae and in the cellular reactions.