A number of population groups can be identified where additional needs potentially exist. These groups may have higher rates of substance use than the general population, substance use may be complicated by other health issues, or mainstream drug treatment services may need to be adapted to suit the particular cultural and other characteristics of the population group. Linkages between drug treatment services, other health and social service agencies in the government and non-government sectors are particularly important to meet the needs of clients in these population groups. In some instances such linkages may involve the provision of advice or assistance relating to clients being care for within other health sectors who also have drug use problems; in other instances linkage may involve connecting clients of drug treatment services with agencies that can meet their additional needs.