We report on measurements of the population of Rydberg states of Na in a constant electric field that result when 300-K blackbody radiation induces transitions from initial states with m=0,1 to neighboring states. Our measurements included comprehensive ranges of initial states ([Formula Presented]=24–29), repopulation times ([Formula Presented]=0–50 μs), and fields ([Formula Presented]=175–712 V/cm). We find that the population is redistributed nonuniformly among states neighboring the initial state, reflective of sharp resonances between the states. By comparing calculations of transition probabilities in Na to the data for [Formula Presented]=200 V/cm we were able to identify the populated states. Comparisons with calculations in H reveal that these resonances are hydrogenic. © 1997 The American Physical Society.