Topical FK506 has recently been shown to have an anti-inflammatory effect in vivo in humans. In this study its effects in contact dermatitis were studied in the guinea pig model. Topical FK506 suppressed both irritant and allergic patch-test reactions. The most prominent suppressive effect was seen when skin sites were pretreated with FK506. Topical FK506 did not impair the induction of contact allergy as assessed by challenges, although it suppressed local lymph node cell accumulation during contact allergy induction. Topical FK506 may hold promise as a treatment for skin disorders that respond to oral FK506 or cyclosporin A.