This paper presents measurements of SO2 flux and ash leachate chemistry from Mt. St. Helens volcano during the period May 18 to July 22 which are in contrast to similar data from before May 18. Comparison of post-18 May SO2 data with similar data from other volcanoes leads to the conclusion that between 15 and 25 May the SO2 flux reached typical magmatic levels. Ash leachate chemistry from the eruption of 18 May, 22 June and 22 July also indicate a large magmatic gas component. Concentrations of Cl- and SO2-4 on May 18 ash increase with distance from the volcano and decrease with time. Leachate chemistry is used to estimate that a minimum of 2.4 ?? 105 tons of S were released on May 18. Low F concentrations on the ash, though increasing, present to health hazards. ?? 1981.