He was a regular member of the Dutch national team. He played for them in the 1973 FIBA Amateur World Series, 1975 European Championship (Silver Medal) and 1977 European Championship (Silver). In the 1978 Amateur World Series, he was 3 for 29 with four walks (tied for the team lead), a double, steal, three runs and two RBI. Starting in left, he had 10 putouts an no errors. He also backed up Arnould Smith at third and had one putout, eight assists and no errors there.
Horeman also played for the Netherlands in the 1979 European Championship (Silver), 1980 Amateur World Series and 1982 Haarlem Baseball Week (being named Dutch MVP). He was with the Netherlands when they finished 4th in the 1983 Intercontinental Cup; it would be another 23 years until they won a medal in the Intercontinental Cup. He also won Silver with them in the 1983 European Championship.