It is shown that gravitational waves generated by close binaries in our galaxy will lead to stellar scintillation. This scintillation seems to be large enough to be detectable with sensitive photocounters in space. With two observation stations separated by a sufficiently large distance in space, it should be also possible to measure the space-time correlation of the predicted scintillation effect and, hence, the propagation velocity of gravitational waves. It is believed that quasars, depending on their state of gravitational collapse, can emit a large amount of gravitational radiation. Under certain assumptions, one can show that the gravitational waves emitted by quasars may result in large brightness scintillation of far distant quasars. The observations of quasars seem to support the theoretically-predicted brightness fluctuations and characteristic fluctuation times. Finally, the question of gravitational background radiation in the universe is considered in connection with the recently discovered 4°K electromagnetic black-body radiation.