The patch test--who should and should not use it and why.

Since its introduction into medicine by Joseph Jadassohn in 1895, the patch test has proven its supreme value in tens of thousands of cases and in research. But emphasis must be placed on the grave errors which can occur when the test is used improperly. Errors are common in the direction of both false positives and false negatives. Common causes of errors are described in detail. The conclusion is drawn that this valuable test had best be used only by those who have been adequately trained and who can apply it regularly on a sufficiently large number of selected patients.