This chapter reviews additional considerations for slug tests performed in fractured and naturally heterogeneous formations, and tests performed in the presence of light nonaqueous phase liquids. The work of J. S. Y. Wang et al. is based on the assumption that the slug-induced flow occurs over the entire plane of the fracture. The form of Equation reveals that it will be challenging to obtain a reasonable K estimate from a slug test in a formation in which the linear flow model is an appropriate representation of the governing physics. Slug tests in small-diameter wells can be a useful means of acquiring detailed information about spatial variations in hydraulic conductivity at a scale of relevance for contaminant transport investigations. A valuable application of slug tests is to assess well conditions and how they are changing with time. Standard models for slug tests in confined formations can then be used to analyze the response data and estimate the aperture of the fracture.