Endocrinology--the way we were: a personal history of somatomedin.

Fifty years ago there was no practical method for measuring growth hormone (GH) activity in human plasma. In an attempt to develop such an assay, it was determined that much of the action of GH in vivo on rat cartilage was mediated by a serum factor that was first known as sulfation factor, and later as somatomedin and insulin-like growth factor. This narrative describes my experience and that of others in this important area of endocrine research.