An unidentified Beechcraft Bonanza passed within 50 feet overhead Piper PA28, VH-JIO. At the time the PA28 was flying in a north westerly direction at 3500 feet and the Bonanza was flying in a north easterly direction. Visual meteorological conditions prevailed. The two pilots in the PA28 did not see the other aircraft until it was too late for evasive action. It is possible that the Bonanza pilot did not see the PA28 because there was no obvious attempt to evade. Significant Factors The following factors were considered relevant to the development of the incident: 1. The pilots in the PA28 did not see the other aircraft until it was too late for evasive action. 2. It is possible that the pilot in the Bonanza did not see the PA28. 3. It is probable that pilot lookout was inadequate.