An orogastric aspiration technique is presented for the estimation of pentagastrin stimulated gastric secretion in the anaesthetised dog. Reference values for volume, pH and hydrogen ion output, 'acidity' and hydrochloric acid output, chloride, sodium, potassium and pepsin outputs were measured and calculated in 23 clinically healthy dogs. It was concluded that 30 and 45 minute hydrogen ion, hydrochloric acid and chloride peak outputs were the most suitable parameters for the acid secreting capacity of the parietal cells. Reference values for 30 and 45 minute peak outputs were respectively 1.63 to 3.61 and 1.50 to 3.35 mmol per hour per kg0.75 (hydrogen ion), 1.86 to 3.64 and 1.65 to 3.42 mmol per hour per kg0.75 (hydrochloric acid) and 2.35 to 4.13 and 1.98 to 3.91 mmol per hour per kg0.75 (chloride). Reproducibility of pepsin outputs was so poor that they cannot be used as parameters for gastric secretory capacity.