Increased atmospheric CO2 may affect the physiological response of natural trees to drought. We examined radial growth rates developed from five western juniper chronologies to determine if post-drought growth responses have changed. Using prior year October to current year June precipitation from 1896--1998, we identified drought recovery years as having standardized scores (z-scores)>0 and preceded by a year with a z-score <-0.6. We defined our analysis by an early period, 1896--1930, when atmospheric CO2 concentrations were close to preindustrial levels, and a late period, 1964--1998, when concentrations were substantially higher. Mean growth index values of recovery years between early and late periods were significantly greater (p<0.05) for four of the five sites, and for all sites combined. These results are consistent with drought-ameliorating effects of CO2 shown by controlled laboratory studies and suggest that rising levels of atmospheric CO2 may impact western juniper growth rates. ¿ 2001 American Geophysical Union