The effect of an ionized or un‐ionized background on magnetohydrodynamic instabilities in a Z pinch is considered. It is shown that the growth rate may be reduced by at least one or two orders of magnitude even though the background pressure is small compared with the pinch pressure. The stabilizing effect of launching shocks in the background gas is considered qualitatively. It is shown that it is theoretically possible to construct equilibria such that confinement for a Lawson time can be attained, but only for backgrounds of roughly liquid density. Also, it is shown that lightning discharges are stabilized by the presence of the background atmosphere.