1. Gastric emptying studies in small laboratory animals are hampered by the deficiency of a technique that is non-invasive and repeatable. The aim of the present study was to adapt the non-invasive [13C]-octanoic acid breath test, which has been validated in humans, to assess both liquid and solid gastric emptying in the mouse. 2. Gastric emptying rates were investigated for a liquid meal (Intralipid; Kabi Pharmacia AB, Stockholm, Sweden; n = 7) and two solid meals (egg yolk and mouse chow; n = 7) incorporating [13C]-octanoic acid. All meals were analysed for natural enrichment of [13C]. Mathematical analysis of the 13CO2 excretion rate allowed the determination of gastric emptying parameters. 3. Gastric emptying of Intralipid was more rapid than egg yolk (P < 0.0001). Gastric emptying of mouse chow could not be assessed due to intragastric separation of [13C]-octanoic acid and natural [13C] enrichment of the pellet. 4. The [13C]-octanoic acid breath test can reproducibly assess both liquid and solid gastric emptying non-invasively in the mouse. This method can now be used to assess gastric emptying in drug studies and disease studies for which there are established mouse models.