The Dunning R-3327-H is a well-differentiated transplantable rat prostatic adenocarcinoma that contains both hormone-sensitive and -insensitive cells. The component composed of hormone-insensitive cells has been permitted to grow in a castrated male, and a new slow-growing, well-differentiated hormone-insensitive subline of the tumor has been established and designated R-3327-HI. In addition, a rapidly growing hormone-insensitive anaplastic tumor has been developed, R-3327-AT. These three tumor lines have been characterized, and their histological and biochemical profiles are compared.