Background (13) C-Acetate labeled meals are widely used to determine meal emptying by means of analyzing resulting (13) CO(2) exhalation dynamics. In contrast to the underlying metabolic processes, only few (13) C breath test meal emptying studies have focused on intragastric processes that may alter (13) CO(2) exhalation. This work assessed the effect of enhanced gastric secretion on the reliability of half emptying time (t50) measurements by (13) C-acetate breath test. Methods (13) CO(2) exhalation data were acquired in a double-blind, randomized, cross-over gastric emptying study in 12 healthy volunteers receiving either pentagastrin or placebo intravenously. The standard method proposed by Ghoos et al. was applied to calculate t50 (t50_Ghoos) from (13) CO(2) exhalation data, which were compared and tested for agreement to meal half emptying times (t50_MV) from concurrent recorded MRI (magnetic resonance imaging) volume data. In addition, the accumulated gastric secretion volumes during infusion as detected by MRI (AUC_SV(60) ) were correlated with the corresponding cumulative percent (13) C doses recovered (cPDR(60) ). Key Results t50_Ghoos and t50_MV showed a linear correlation with a slope of 1.1 ± 0.3 (r(2) = 0.67), however, a positive offset of 136 min for t50_Ghoos. No correlation was detected between AUC_SV(60) and cPDR(60) (r(2) = 0.11). Both, breath test and MRI, revealed a prolonged t50 under pentagastrin infusion with median differences in t50_Ghoos of 45[28-84] min (P = 0.002) and t50_MV of 39[28-52] min (P = 0.002). Conclusions & Inferences This study suggests that (13) CO(2) exhalation after ingestion of a (13) C-labeled liquid test meal is not affected by stimulated gastric secretion, but is rather reflecting the dynamics of meal or caloric emptying from the stomach.