Creative ideas are essential to original concept generation and ultimately innovation. But where and when do these vital creative ideas occur during product innovation and more importantly how can they be influenced? The following paper describes an industrially based study of several innovation projects following the actual processes of professional designers. Some ideas from the early brainstorm can be traced all the way through to concepts that are selected at the company's stage-gate. Those early ideas are marked as 'appropriate' which provides an objective evaluation of the influence of any prescribed creative stimuli being used during the brainstorm sessions in relation to the output of the innovation process. The results showed that the frequency of idea production remained roughly constant during the first 30 min but steadily reduced after this period. However, the number of 'appropriate' ideas decreased rapidly, where 75% of the appropriate ideas in the first 30 min had been expressed after just 15 min. By introducing various forms of stimuli to the groups, the frequency of idea generation was maintained and in many cases increased. The stimuli were also shown to help generate more appropriate ideas which were included within concepts proposed at the stage-gate.