Summary The pressure response of a double-porosity reservoir to a slug test in a fully penetrating well with wellbore storage and skin is presented. Pseudosteady-state matrix flow and transient matrix flow with and without matrix skin are considered. Three kinds of type curves are discussed: early-time log-log, intermediate-time semilog, and late-time log-log. Pressure distribution around the active well and the prospects of interference slug testing are considered. The early-time response of the slug test depends on the presence of wellbore skin; hence, two kinds of early-time type curves are presented. When the active well has wellbore skin, the early-time correlating parameter is the product of the skin and the dimensionless storage, resulting in a new log-log type curve. When wellbore skin is not present, the early-time response is proportional to the square root of time with dimensionless storage as the correlating parameter. The intermediate-time semilog type curves are applicable when wellbore skin is not present, or CDe2S>104. The double-porosity effects are significant in the late-time log-log format, but the flat portion of the pressure response occurs at dimensionless pressures less than 0.01. The radius of investigation of the slug test in a double-porosity system is also examined with and without wellbore skin at the active well. Interference responses and pressure profiles are presented. Although the presence of wellbore skin reduces the magnitude of the dimensionless pressure responses at observation wells, the detectable radius of investigation does not significantly depend on wellbore skin. Interference slug testing in a double-porosity system requires high-precision pressure-recording tools in the observation wells because the double-porosity effects occur at small dimensionless pressures. Transient matrix flow without matrix skin reduces the double-porosity effects and limits the use of type curves for determining λ and ω. The slug-test double-porosity effects in a reservoir with transient matrix flow with fracture skin and pseudosteady-state matrix flow are similar.