  The results of tests of 1'' vacuum phototriodes in a magnetic field up to 4.5
T are presented. It was found that output amplitude decreases by about 6 % per
tesla in the magnetic field range from 2.0 to 4.0 T. For devices with an anode
mesh pitch of 16$\mu$m, the output amplitude at 4.0 T is 30 % lower than that
at zero field.
