The spontaneously diabetic adult male Abyssinian-Hartley guinea pig develops bladder hypertrophy and voiding dysfunction. In contrast to animals with chemically induced diabetes, this animal demonstrates changes in bladder function in the absence of diuresis. The diabetic guinea pigs void a total daily volume similar to that of control animals, but have a greater mean volume per void and a longer interval between voiding. Cystometry demonstrates that the diabetic guinea pig produces greater intraluminal bladder pressure, but maintains voiding pressure for a shorter interval. A significantly decreased contractile response of the diabetic bladder base may be responsible for the bladder hypertrophy and voiding dysfunction.