JHC> [I'm a little bit scared that maybe I've missed one out and two of the above are isomorphic, but I don't think so.] My memory is that most of the order sixteen groups can be distinguished by looking at the spectrum of element orders, but there are one or two pairs that have the same spectrum and require additional properties to split. Specturm of element orders: for Z16, there is 1 element of order 1, 1 of order 2, 2 of order 4, 4 of order 8, 8 of order 16. [1 1 2 4 8]. Rich rcs@cs.arizona.edu