I have just received from Ann Harrison the sad news that Dave died last Dec. 21. I suspect that most of the younger practitioners of category theory are not aware of Dave's contributions to the subject. Not in the sense of having actively worked on it, but of having encouraged it in the very early days. When he came to Penn he taught a course in homological algebra that used categories extensively. In point of fact, I had never heard of a category before taking that course. Then he was one of the main organizers of the La Jolla conference in 1965 that was the first ever major international conference in categories. (The first conference that I am aware of was the midwest category meeting that Saunders Mac Lane organized in April (I think) of the same year, a few months earlier. But the participants consisted only of a handful of people from Urbana and Chicago.) For anyone who wishes to write Ann, her address is 12 Striper Lane, Chatham, MA 02633. Michael