The manual is intended to provide users of PROBE computer code with necessary background information and assistance for successful use.PROBE (PROgram for Boundary Layers in the Environment) can be classified as an "equation solver for one-dimensional transient, or two dirnensional steady, boundary layers". Typical examples of such boundary layers are the Ekman layer and the developing channel flow. A major difficulty in these kinds of flow is to characterise the turbulent mixing in mathematical terms. PROBE embodies a two-equation turbulence mode!, the k - E  model, which calculates mixing coefficie´nts. Together with two momentum equations the turbulence mode! forms the basis for the hydrodynamical part af the mathematical model. In the basic version six additional variables are provided for: heat energy, salinity, and four concentrations. The number of concentrations can, of course, easily be increased when needed.