Brazil is one of the biggest markets for motorcycles around the world. New emission legislation is taking place leading to the release of new motorcycles equipped with catalyst converters and electronic injection system. Although emission formation is quite understood regarding light duty vehicles, it is necessary to do further studies for motorcycles vehicles. This paper presents the results of an investigation regarding regulated and unregulated emissions (aldehydes and ammonia) from four 4-stroke gasoline motorcycles. Three motorcycles equipped with three-way catalytic converters and one EURO 1 motorcycle, without catalyst system, were tested on a chassis dynamometer according to the 97/24/EC drive cycle. Regulated emissions (CO, HC, and NOx) were measured with 7000 series Horiba benches and unregulated emissions were analyzed by a SESAM series AVL FTIR (Fourier Transform Infrared Analyzer), including pre- and post-catalytic converter data acquisition. Test results have shown that catalytic converters designed to reduce regulated emissions from gasoline-powered motorcycles produce ammonia emissions as a by-product of catalytic conversion. Comparative emissions results for all motorcycles tested are presented, including analyzes and comments of the catalytic conversion performance (pre- and post-cat) for aldehyde emission. The paper concludes that a significant increase of ammonia emission levels was observed in most of the motorcycles studied.