The computer code Samplan for multiarea hydrothermal scheduling has been extended to take transmission constraints into account, by using a simplified power flow model. In Samplan the system has a simplified representation by a subdivision into areas. Each area is represented by a lumped subsystem consisting of one reservoir and one power station. The transmission between any pair of areas is represented by a single line. In previous versions of Samplan the transmission lines have been modelled as a transport model, with a loss factor and a capacity limit. This usually does not fulfil basic electrical power flow laws. Since the algorithm used in Samplan does not allow complicated nonlinear models, we represent the power transfer constraints by linear constraints based on power transfer distribution factors (PTDFs). The report gives an overall description of the implementation, with a few tests that indicate that the implementation is correct and works. The examples indicate that the introduction of the transmission constraints may not change the reservoir release strategies much from the previous version of Samplan. However, the solutions should now be closer to feasibility in terms of power flow correctness. The goal of the work carried out was to demonstrate the feasibility of including PTDF constraints in Samplan, with emphasis on principles. For the implementation to become a fully working tool, the data structures must be more refined, especially with respect to time dependence. Losses are not included; this must be added by an approximate procedure.