To explore whether market reforms in a health care system affect medical professional ethics of hospital-based specialists on the one hand and physicians in independent practices on the other. Qualitative interviews with 27 surgeons and 28 general practitioners in The Netherlands, held 2-3 years after a major overhaul of the Dutch health care system involving several market reforms. Surgeons now regularly advertise their work (while this was forbidden in the past) and pay more attention to patients with relatively minor afflictions, thus deviating from codes of ethics that oblige physicians to treat each other as brothers and to treat patients according to medical need. Dutch GPs have abandoned their traditional reticence and their fear of medicalization. They now seem to treat more in accordance with patients' preferences and less in accordance with medical need. Market reforms do affect medical professional principles, and it is doubtful whether these changes were intended when Dutch policy makers decided to introduce market elements in the health care system. Policy makers in other countries considering similar reforms should pay attention to these results.