Significant advances in Alzheimer's disease (AD) research require definitive, reproducible findings from all employed paradigms. Recently, the existing in vitro data addressing the possible contribution of beta-amyloid protein to AD neuropathology have been the subject of controversy. We summarize and interpret existing data and discuss relevant methodological issues. We suggest that in vitro data support the conclusion that beta-amyloid peptides decrease the viability of cultured neurons and that this effect can be enhanced by subsequent insults.