Despite the growing importance of radio as an advertising medium in The Netherlands, there is very little research available on the impact of radio advertising and how to influence it. We designed an experimental survey to learn how to influence the impact of a radio commercial. Factors included in our study were length of the spot, length of the advertising block it is aired in, the position within the block and the likeability of the spot. Results indicate the length of the block as well as block position (to a somewhat lesser degree) influence impact: the longer the block, the lower the impact of each individual spot - except when aired first in a block, which is the ultimate goal when trying to insure impact. Furthermore, the spot length had some influence on impact. Spots longer than forty seconds scored significantly higher impact. Nevertheless there was an interaction effect between spot length and likeability. Likeable ads were longer or longer ads were more likeable. Even more, the brand image seemed to correlate with likeability. However, it seems that product and/or brand involvement cause this correlation.