1. Simultaneous 24 h intragastric acidity and plasma gastrin concentration profiles were determined in 35 healthy young women and 96 healthy young men. 2. The females had a consistently lower median hourly intragastric acidity, and a higher median hourly plasma gastrin concentration, throughout the 24 h. 3. The 24 h integrated intragastric acidity was significantly lower in the female group (females, 485 mmol.h.l-1; males, 842 mmol.h.l-1. P less than 0.001). The 24 h integrated plasma gastrin concentration was significantly higher in the female group (females, 407 pmol.h.l-1; males, 185 pmol.h.l-1; P less than 0.001).