[en] This study develops a model for the source of radio recombination line emission from the galactic plane. The model is based mainly on recombination line spectra observed in the direction of the supernova remnant 3C391. The H157α recombination line was observed and used with the H92α spectrum observed by Cesarsky and Cesarsky (1973) to obtain a model consistent with both spectra. Other criteria--such as the 80 MHz optical depth, the contribution to the thermal continuum temperature, and ionization rates--were also considered. Four models were studied: a cold region illuminated by 3C391; an isolated cold region; a group of hot, dense H II regions; and a low density H II nebula. Of these, the best model is a small (approximately 85 pc diameter) H II region with a temperature of 7500⁰K and an average electron density of 10^-3 cm^-3. The H157α spectrum in the direction of the pulsar 1858 + 03 was also observed. It was found that it is probable that one of the recombination line nebulae lies along the line of sight to the pulsar. In this case the pulsar would be at a distance of 2.6 kpc in order for its dispersion measure to agree with the measured value of 402 pc cm^-3. The large scale distribution of the H II nebulae was also studied. The results of available radio recombination line spectra surveys from the galactic plane suggest that they exist within an annular region which extends from 4 to about 8.7 kpc from the galactic center