The high figures of occupational asthma worldwide necessitate the intensification of appropriate primary, secondary, and tertiary preventive measures. Based on new scientific data on dose-response relationships as well as our own experience and ethical aspects, we focus on medical surveillance within the framework of secondary prevention. We propose that medical surveillance programs be mandatory for workplaces/occupations with an asthma incidence of > or = 200% than that of the general population. Medical surveillance programs are recommended if asthma frequency is elevated but below 200%. A stepwise approach of monitoring workers at risk for developing occupational asthma including a screening by questionnaire and a personal interview and diagnosis confirmation is presented. In addition, we briefly comment on the management of affected subjects.