In August, 1974, the definition of the STOP sign in New South Wales was changed to correspond with accepted international practice. Driver behaviour was observed at ten open, free-flowing, orthogonal intersections posted with STOP signs and at two similar intersections posted with GIVE-WAY signs. Observations were carried out once before and twice after the date of the change. The behaviour of the drivers approaching the signs was recorded in relation to that of the other drivers with whom they interacted. The proportion of drivers who actually stopped at the STOP signs initially increased and then fell below the original level. The final proportion was similar to that observed at the GIVE-WAY signs which were not affected by the change in regulations. The proportion of drivers who yielded as required at STOP signs showed little initial change, but subsequ_ntly increased. A similar pattern was observed at GIVE-WAY signs and in the final survey the porportions were approximately equal. The marked similarity in driver behaviour between the two sign types might suggest the need for a re-evaluation of the placing of STOP signs.