Over the past decade increased attention has focused on the role of primary care physicians in the treatnient of dnig atid alcohol problems. Compelling aigiments have been proffered in their slipport iiicliiding high prevalence levels witliin coniniiinity poprilatioiis and frequency of presentation in primary care settings. In addition, ready access, !lie notistigmatizing setting, and proven efficacy of physician-delivered early intervention add further weight to primary care provider involvement. However, a complex relationship exists between treatnient providers and potential recipients-and greater involvement is hampered by niinieroiis factors. For instance, substantial evidence suggests that primary care providers are less than entliusiastic, are inadequately infomed, and perfomi poorly with regard to identification and treatment of dnig and alcohol problems. These deficits are examined from several perspectives. Doctors' willingness to intervene (IWI) is discussed in relation to a recently developed model ivliicli encompasses fortr key components: the doctor factor, the patient factoG the context factor, and the doctor-patient interaction factor. Some components of this model are disciissed in relation to barriers fo wider involvement by primary care physicians. The extent to, wliicli poor knowledge levels may impact ripon provision of treatment is examined and discussed in light of recent Aiistralian and Canadian siirveys of primary care pliysicians' knowledge and attitudes, Finally, consideration is given to a novel application of Skog's (1) social contagion theory, to tlie effect that when patients are siiccessfiilly coiinseled to reduce their alcohol consumption, they influence their social contacts to do likewise. Such an effect would multiply the benefits to the community arising from the provider5 siiccessfii I detection and management of an individiial patient's alcohol or other dnig-related problems. A n experimental protocol to test this theory is described.KEY WORDS: primary care; intervention; substance use; drug and alcohol problems; treatment.'Based on a paper presented at