  We investigate the role of cosmic rays from young galaxies in heating and
ionizing the intergalactic medium (IGM) at high redshift. Using the IRAS
observations at $60 \mu m$, we estimate the cosmic ray luminosity density at
the present epoch. We consider various forms of luminosity evolution in
redshift and calculate (a) the thresholds corresponding to the upper limits of
Gunn-Peterson optical depth, (b) the Compton $y$ parameter for an IGM heated by
cosmic rays and compare with the upper limits from COBE measurements and (c) an
estimated limit from the integral of metal enrichment. We show that certain
models, with rather strong evolution and early formation of galaxies, allow
reionization of the IGM, consistent with all known constraints.
