A tripod-mounted correlation spectrometer was used to measure SO2 emissions from Pu`u `O`o vent, mid-ERZ, Kilauea, Hawaii between Episodes 33 and 34 (June 13 to July 6, 1985). In 24 repose days, 906 measurements were collected, averaging 38 determinations/day. Measurements reflect 13% of the total 576 hours of the repose and 42% of the bright daylight hours. The average SO2 emission for the 24-day repose interval is 167??83 t/d, a total of 4000 tonnes emitted for the entire repose. The large standard deviation reflects the "puffing" character of the plume. The overall rate of SO2 degassing gently decreased with a zero-intercept of 44-58 days and was interrupted by two positive peaks. The data are consistent with the gas emanating from a cylindrical conduit of 50 meter diameter and a length of 1700 meters which degasses about 50% of its SO2 during 24 days. This is in support of the Pu'u `O`o model of Greenland et al. (1987). 36 hours before the onset of Episode 34 (July 5-6, 1985), elevated SO2 emissions were detected while the magma column was extremely active ultimately spilling over during dome fountaining. A "mid-repose" anomaly of SO2 emission (June 21-22, 1985) occurs two days before a sudden increase in the rate of summit inflation (on June 24, 1985), suggesting magma was simultaneously being injected in both the ERZ and summit reservoir until July 24 when it was channelled only to the summit reservoir. This implies degassing magma is sensitive to perturbations within the rift zone conduit system and may at times reflect these disturbances. Periods of 7-45 min are detected in the daily SO2 emissions, which possibly reflect timing of convective overturn in the cylindrical magma body. If the 33-34 repose interval is considered representative of other repose periods, the ERZ reposes of Jan 1983-Jan 1986 ERZ activity, contributed 1.6 ?? 105 tonnes of SO2 to the atmosphere. Including summit fuming from non-eruptive fumaroles (2.7 ?? 105 tonnes SO2); 28% of the total SO2 budget from Kilauea between Jan 1983 to Jan 1986 was contributed by quiescent degassing, and the remainder was released during explosive fountaining episodes. ?? 1988 Springer-Verlag.