A treatment is given of the M/G/1 queue with interruptions of Poisson incidence occasioned either by server breakdown or the arrival of customers with higher priority. Interruption times and priority service times have arbitrary distribution. After pre-emptive interruption, ordinary service is either repeated or resumed. The time dependent behavior of the system is discussed in a complete state space and the joint density in all system variables of this space is constructed systematically from the densities associated with a set of simpler first-passage problems. Equilibrium distributions are available as limiting forms and server busy period distributions obtained.