A circuit arrangement for ignition systems for detecting an arc voltage at a spark plug has an ignition coil having a primary side on which the arc voltage is transformed and also having a primary winding, an ignition switch located in series with the primary winding of the ignition coil, a pnp transistor working as a voltage converter and having a control stage so that the arc voltage transformed on the primary side activates the control stage. The transistor is connected on an emitter side to a connection between the primary winding and the ignition switch. The pnp transistor is connected on a base side to a battery voltage. A resistor is assigned as an emitter follower to the pnp transistor. A measuring element is formed as a resistor. The transistor with its collector connection feeds to the measuring element a collector current which is proportional to the arc voltage.