Using the radio wave and energetic particle experiments on the Wind spacecraft, we examine how the radio flux density of interplanetary type III bursts depends on the flux and energy of the energetic electrons. We derive the relationship between them, first by giving detailed radio and electron characteristics of one type III burst, and then using the results of similar analyses of 10 bursts. The times of commencement of the radio waves from decametric to kilometric wavelengths, in relation to the onset time of Langmuir waves, demonstrate forcibly that the initial type III radiation is at the fundamental and not the harmonic. Near and after the time of peak flux density the radiation could be either at the fundamental or the harmonic. In our theoretical analysis we examine this point, i.e., how the emissivity of the fundamental and harmonic at the time of peak flux density depends on the beam properties. The data of the 10 events are in good accord (rc≈0.9) with the theoretical relation for fundamental emission, but in disaccord with the theoretical relation for harmonic radiation. For the 10 bursts we find poor correlation between the radio flux density and the electron flux N(E∥) at the energy E∥ estimated to be that of the two-stream instability. However there is excellent correlation when N(E∥) is weighted by E∥ to a high power. From the best fit, we find rc≈0.96 when N(E∥) is replaced by E∥3.98N(E∥). Finally, we infer the efficiency of energy conversion from the kinetic energy of the electron beam to fundamental emission, and examine the attenuation of the peak emission within the source. ¿ 1998 American Geophysical Union