The significance of paranasal sinusitis as a local disease and its importance as a focus of infection in relation to a variety of systemic diseases are generally recognized. The pertinent problem at present is to discover the sinusitis when it exists, and this involves an evaluation of the evidences of infection as disclosed by the methods of investigation employed. Recognition of sinusitis is simple when there are local manifestations, but it is not generally understood that an infection of the paranasal sinuses may exist in the absence of local manifestations. Watson-Williams 1 has written of such sinusitis as "latent or occult infections" ; Harper 2 has called this type of sinusitis "hidden infection," and Sohval and Som 3 have used the term "masked sinusitis" in reporting cases of obscure fever. It seems best to consider these infections of the paranasal sinuses as silent so far as symptoms, local manifestations and apparent relation to systemic diseases are concerned.Thus, the paranasal sinuses must be investigated regularly as a possible source for headache or fever, especially when following infections of the upper respiratory tract, or for a focus of infection, even though no symptoms or physical evidences of sinusitis are presented.A complete investigation for the purpose of discovering an infection of the sinuses entails a direct examination of the upper respiratory tract, transillumination and roentgenologic study of the sinuses and diagnostic lavage of the maxillary antrums and the sphenoid sinuses. The comparative value and accuracy of these diagnostic methods have been the subject of much argumentative discourse among rhinologists in recent years. Unfortunately the conclusions and opinions of various authors have differed greatly in respect to some of these points, par-From the Laryngologic Service of Dr. Rudolph Kramer and the laboratories of the Mount Sinai Hospital.