Measurements of the intensities of plasma lines in the radar incoherent-scatter spectrum are reported. The measurements were performed with the UHF radar at Millstone Hill, Massachusetts, on February 9, 1969. Theory of the plasma lines is reviewed, and problems of data interpretation are discussed. The plasma-line intensities are interpreted in terms of photoelectron upward and downward flux components at 560 km. The net upward flux there is found to be 3.6 × 108 cm−2 sec−1. From the measured fluxes and a simplified picture of photoelectron transport, the escape flux and the arriving conjugate-point flux are found. In addition, the opacity of the protonospheric field tube connecting Millstone Hill and its conjugate point is estimated as 0.85 for photoelectrons.