Studies have shown that a large proportion of motorcycle accidents involve the failure of a road-user to see an approaching motorcycle. It is estimated that in Britain about one third of all collisions between motorcycles and other vehicles involve a visual or perceptual difficulty. Similar findings exist in other countries. The majority of such accidents occur in daylight but perceptual difficulties are also a prominent feature of night time collisions. This paper describes a series of trials designed to assess measures which might alleviate these problems by modifying the appearance of motorcycles. The use of existing and additional lighting and fluorescent materials, intended to assist the detectability and identification of motorcycles in traffic, was examined in both daylight and darkness. The results demonstrated ways of increasing the conspicuity of motorcycles in a wide range of daylight situations, but they also showed that some widely-used measures are not effective. At night, detectability was found to depend on the intensity and beam-pattern of the motorcycle's front lighting, but identification was aided by lighting used in addition to the standard headlamp.