Abacavir hypersensitivity (ABC HSR) is a treatment-limiting adverse event 
associated with the use of the antiretroviral medicine, abacavir. The objective 
of the ABC HSR pharmacogenetics program was to identify clinically useful 
genetic risk factors to predict an individual patient's risk for ABC HSR. The 
major histocompatibility complex allele, HLA-B*5701, was identified 
retrospectively and confirmed with independent sample sets. The clinical utility 
of prospective HLA-B*5701 screening was demonstrated in a blinded randomized 
clinical trial and in open-label cohorts. Screening has been incorporated into 
clinical practice and the ABC HSR pharmacogenetics program has been highlighted 
as a success by pharmacogenetics researchers. Important lessons from this 
pharmacogenetics program will be discussed in this paper.