  Previous surveys by Baumert and Lopez and Sanchez have resolved the existence
of cyclic (v,k,lambda) difference sets with k <= 150, except for six open
cases. In this paper we show that four of those difference sets do not exist.
We also look at the existence of difference sets with k <= 300 and cyclic
Hadamard difference sets with v <= 10,000. Finally, we extend an earlier search
of the second author to show that no cyclic projective planes exist with
non-prime power orders up to two billion.
