The feasibility of using item response theory (IRT) as a psychometric model for the Graduate Record Examination (GRE) Aptitude Test was addressed by assessing the reasonableness of the assumptions of item response theory for GRE item types and examinee populations. Items from four forms and four administrations of the GRE Aptitude Test were calibrated using the three-parameter logistic item response model. Three equating methods were compared in this research: equipercentile equating, linear equating, and item response theory true score equating. Various data collection designs (for both IRT and non-IRT methods) and several item parameter linking procedures (for the IRT equatings) were employed. The IRT methods produced quantitative scaled score means and standard deviations that were higher and lower, respectively, than those produced by the linear and equipercentile methods. The most notable finding in the analytical equatings was the sensitivity of the precalibration design (used only for the IRT equating method) to practice effects on analytical items, particularly for the analysis of explanations item type. Since the precalibration design is the data collection method most appealing (for administrative reasons) for equating the GRE Aptitude Test in a test disclosure environment, this sensitivity might present a problem for any equating method. (PN)