A clustering method that exploits USEARCH to assign sequences to clusters. UCLUST is superior to CD-HIT. It is usually significantly faster, uses significantly less memory, can cluster at lower identities and is more sensitive. While CD-HIT often fails to identify the closest cluster, or overlooks that a match is possible (false negative), UCLUST rarely misses a match and in most cases finds the best possible match. UCLUST also enables rapid clustering of much larger numbers of sequences.