We present a framework for high-level design validation using an ef.cient register-transfer level (RTL) automatic test pattern generator (ATPG). The RTL ATPG generates the test environments for validation targets, which include variable assignments, conditional statements, and arithmetic expressions in the HDL description. A test environment is a set of conditions that allow for full controllability and observability of the validation target. Each test environment is then translated to validation vectors by .lling in the unspeci.ed values in the environment. Since the observability of error effect is naturally handled by our ATPG, our approach is superior to methods that only focus on the excitation of HDL descriptions. The experimental results on ITC99 benchmark circuits and an industrial circuit demonstrate that very high design error coverage can be obtained in a small CPU times.