Explores the potential of a hybrid intelligent system in supporting marketing strategy development. First, a hybrid intelligent system for developing marketing strategy, called MarStra (developed by the author), is outlined. Then discusses the real-world tests of MarStra with marketing directors in five large UK companies. Empirical evidence from the companies involved indicates that MarStra is very helpful and useful in: providing strategic analysis guidance; coupling strategic analysis with managerial judgement; helping strategic thinking; dealing with fuzziness and uncertainty; and supporting group assessment of strategic marketing factors. The intelligent outputs generated by MarStra were reported to be surprisingly accurate, mostly sound and useful prompts.