As of September 2015, the main PBS website, PBS.org, does not stream the Doc Martin program. The site does, however, offer limited information about the program.
Doc Martin is a British show distributed in the United States by American Public Television. PBS.org notes that local affiliate stations may show the program and that their websites may, therefore, have bonus content. This might include some episodes, but it does not cover streaming of a full series.
Viewers interested in watching the series can check their local stations for availability or use an online streaming service such as Netflix to access episodes.