Cryptophyceae are important group in marine phytoplankton, but little is known about the occurrence and distribution of individual species. Recently, with use of molecular probes and microarray technology, it has been shown that species related to teleaulax spp. or Chroomonas spp. (clades 4 or 6) contributed the most to cryptophycean biomass in the north Sea. for the microarray study, the single probe (clade 4/6) recognizes members of both clades 4 and 6 and thus cannot separate them. Therefore, it was unknown as to whether the cryptophyte community was composed of clade 4, clade 6 or both of them. Here, we addressed this question and increased the genetic diversity of our investigations of cryptophycean diversity in the north Sea by sequencing 18S rRnA clone libraries made from fractionated water samples to examine specifically the picoplanktonic fraction because that fraction was studied in detail in the earlier microarray study. We focused on samples from the spring phytoplankton bloom in 2004 because the microarray signals were the strongest at this time. Excluding chimeric sequences, we detect- ed nine cryptophycean oTUs, seven of which fell into the teleaulax/Plagioselmis branch, whereas two grouped with Geminigera spp. our results indicate that these oTUs, affiliated with clade 4, may be an important component of cryptophyte community during spring bloom in the north Sea