When man considers his environment he should not be surprised that respiratory infections are common. Certainly the respiratory tract represents a portal of entry over which we do not have too much control. Usually we can forego a meal which does not appeal to us or one which we find offensive or suspect of being polluted. Such a choice is indeed limited as concerns the air we breathe. Consequently the list of agents entering by way of this route which can cause disease is long. The filtering capacity of the pulmonary capillary bed is great; therefore in systemic infections, neoplasms, and in other situations a considerable number of factors may give rise to symptoms and increased density by way of roentgenographic record. For lack of time all of the conditions with which viral infections might be confused cannot be discussed. Allergic manifestations, toxic drugs, irritants, fungal and bacterial infections, respiratory