We present three explicit constructions of hash functions, which exhibit a Ž trade-off between the size of the family and hence the number of random bits needed to . Ž . generate a member of the family , and the quality or error parameter of the pseudorandom property it achieves. Unlike previous constructions, most notably universal hashing, the size of our families is essentially independent of the size of the domain on which the functions operate. The first construction is for the mixing propertyᎏmapping a proportional part of any subset of the domain to any other subset. The other two are for the extraction propertyᎏmapping any subset of the domain almost uniformly into a range smaller than it. The second and third constructions handle, respectively, the extreme situations when the range is very large or very small. We provide lower bounds showing that our constructions are nearly optimal, and mention some applications of the new constructions. ᮊ 1997 John Ž .