Although differential diagnostic difficulties seldom arise in cases of "typical" acute trichinosis, the problem is not so simple in mild, subacute, chronic or otherwise unusual ones, which comprise the majority of cases.1 Hall2 lists about fifty diseases or conditions which have been mistaken for trichinosis, yet neither he nor most authors include periarteritis nodosa as one of them in spite of its clinical resemblance to trichinosis. On the other hand, trichinosis is often mentioned with dermatomyositis and other obscure conditions in discussions of the differential diagnosis of periarteritis nodosa. In fact, numbers of cases of periarteritis nodosa have been recognized by the typical histologic lesion at biopsy in cases of suspected trichinosis. In diseases as similar to each other and as variable in their manifestations as trichinosis and periarteritis nodosa, it is surprising that no mention is made in any of the reports we have read of serious