A survey of 4378 significant innovations shows that firms with fewer than 1000 employees commercialised a much larger share than is indicated by their share of R & D expenditures. Innovations per employee have been consistently above average in firms with more than 10 000 employees, and have become so in firms with fewer than 1000. Intersectoral variation in the size distribution of innovating firms can be explained as a function of R & D-based technological opportunities, and of "technological ease of entry" by user firms with principal activities outside the sector.