Odd and even group divisible designs with two groups and block size four

We show the necessary conditions are su6cient for the existence of GDD(n; 2; 4; 1, 2) with two groups and block size four in which every block intersects each group exactly twice (even GDD’s) or in which every block intersects each group in one or three points (odd GDD’s). We give a construction for near 3-resolvable triple systems TS(n; 3; 6) for every n¿ 4, and these are used to provide constructions for several families of GDDs. c © 2004 Elsevier B.V. All rights reserved.