Aims To compare variability of heart rate-corrected QT intervals (QT c ) using three different methods in a study of low-dose oral haloperidol. Methods In a randomized, double-blind, placebo-controlled, crossover trial, we studied QT interval pharmacodynamics of single doses of oral haloperidol (10 mg) in 16 healthy subjects. Heart rate correction of the QT interval was performed using Bazett's, Fridericia's and subject-specific correction methods. The subjectspecific correction was performed using linear mixed modelling of placebo period QT vs RR data from each study subject. Results The subject-specific correction, in the form of QT c = QT/RR a , yielded a correction term a (slope of the log-transformed QT vs RR relationship) that ranged from 0.23 to 0.38 in individual subjects, i.e. the fixed correction term a = 0.5 of Bazett's correction was outside and the fixed correction term a = 0.33 of Fridericia's correction inside the range of individual values. The mean absolute slope of the QT c vs RR regression line using the subject-specific correction was significantly lower than the mean slopes obtained using either Bazett's or Fridericia's corrections. All three methods revealed a statistically significant greater mean QT c on haloperidol than on placebo at 10 h post-drug administration. The mean QT (95% CI) was 421.6 (410.8, 432.4), and 408.4 (398.6, 417.8) on haliperidol and placebo, respectively, using the subject-specific correction method (P = 0.0053). The mean QT c (95% CI) was 425.4 (414.3, 436.5) and 403.1 (394.3, 411.9) on haliperidol and placebo, respectively, using Bazett's correction (P = 1.7 ¥ 10 -5 ) and 423.1 (412.6, 433.6) and 408.2 (398.6, 417.8) on haliperidol and placebo, respectively, using Fridericia's correction (P = 7.7 ¥ 10 -4 ). Raw P-values were calculated using a paired t-test. Bonferroni-corrected P-values were calculated by multiplying the raw Pvalues by 13. Conclusion Haloperidol caused a statistically significant mean QT c prolongation using the three correction methods. The QT c intervals were less dependent on RR intervals using the subject-specific method, thus decreasing the possibility of overor under-correction. The interindividual QT c changes from baseline varied significantly depending on the method of correction used.