The use of advanced recombinant DNA technology has provided an improved understanding of the human AAT deficiency phenotype by providing the amino acid sequence of several variant proteins and by allowing for the production of various cell and animal models to study the molecular and biochemical components of the retention, degradation, and accumulation of these variants in the hepatic ER. Human AAT deficiency will continue to serve as an excellent model for enhancing our current understanding of mechanisms utilized in regulating protein "traffic" in the ER and in elucidating the pathophysiologic components of AAT-related liver disease.