BACKGROUND Due to cross-reactions between unfractionated heparins, low-molecular-weight heparins and sometimes heparinoids, cutaneous delayed hypersensitivity reactions might be a problem for the choice of therapeutic alternative. We report on two cases of sensitization to heparins and heparinoids. METHODS One woman developed localized skin reaction to a low-molecular-weight heparin, then a generalized maculopapular rash when an intravenous injection of unfractionated heparins was performed. The second patient had a localized then extended reaction to a low-molecular-weight heparin and was referred for the choice of a well tolerated method to obtain anticoagulation during a pulmonary surgery. METHODS Patch tests, prick tests, intradermal and subcutaneous tests were performed with several unfractionated heparins, low-molecular-weight heparins, danaparoid and lepirudin in both cases. RESULTS In the first case, tests performed with both heparins and heparinoid were positive and the use of lepirudin was proposed if anticoagulation was necessary. In the second case the subcutaneous danaparoid injection induced a localized reaction on the injection site. Danaparoid injections were continued associated with localized applications of dermocorticoids without any side effect. CONCLUSIONS Cutaneous delayed hypersensitivity reactions occur on the injection site but can also be generalised. Cross reactions might be unexpected therefore skin-tests are necessary to guide the choice of a therapeutic alternative. In case of intolerance to both heparins and heparinoids various solutions may be proposed such as the application of topical corticosteroids on the injection site or the administration of hirudins. There is no cross sensitization between heparins and hirudins, but the use of hirudins is restricted and requires specific monitoring.