The spectrum of AX Monocerotis has been studied on 172 spectrograms covering both the visual regions. The system consists of a rapidly rotating B3 star and a s6mewhat fainter K giant. e P Cygni-like structure at the hydrogen lines of the B star undergoes rapid variations that may be ated to outbursts on the surface of the star. These also may be correlated with irregular light varians of a few tenths of a magnitude. Absorption lines of ionized metals and hydrogen are found to reappear near the same phase of each ital cycle (P = 232.5 days). These lines are interpreted as evidence of gaseous material streaming beeen the two stars. The B star is found to have a mass of 8.6 M0 while that of the K star is only 3.4 M0, though the star is apparently the further evolved. Mass exchange may account for this discrepancy. Weak forbidden iron emission suggests that the whole system is enveloped in a tenuous nebula.