The paper evaluates and interprets the updated scientific and technical information that EPA staff believes is most relevant to the review of primary (health) national ambient air quality standards for sulfur oxides and represents an update of previous staff conclusions and recommendations in the 1982 sulfur oxides staff paper to incorporate more recent information. The assessment is intended to bridge the gap between the scientific review in the EPA criteria document second addendum for particulate matter and sulfur oxides and the judgements required of the Administrator in setting ambient air quality standards for sulfur oxides. The major recommendations of the staff paper addendum include the following: (1) that the health data support the need for sulfur dioxide (SO2) standards; (2) that new data from controlled human exposure studies on asthmatics and atopics warrant consideration of a new short-term (1-hour) standard; (3) that the current primary and secondary standards (annual, 24-hour, and 3-hour) provide substantial protection against effects associated with 24-hour and annual exposures, and some limit on peak exposures of concern for asthmatics; (4) that the relative protection afforded by current vs. alternative standards is an important consideration in determining, what, if any, standards revisions may be necessary.