A statistical analysis assesses the effects of the energy shortage of 1973–74 on ambient air quality in Metropolitan Boston. Standard multivariate regression techniques were used to investigate relationships between measured pollutant levels, meteorological parameters and regulatory controls. The observed long-term decline in ambient sulfur dioxide and total suspended particulate levels from 1970 through 1974 cannot be attributed principally to changes in regional meteorological conditions. Rather, regulatory controls on the sulfur and ash content of fuels burned in the region are implicated. No statistically significant rise in pollutant levels occurred coincident with variances granted on clean-air regulations because of the energy shortage. This was due to simultaneous fuel conservation efforts and the fact that the energy shortage caused shortages of all grades of fuel.