The tumour suppressor gene WT1 encodes a zinc-finger protein, which consists of four C-terminal C2-H2 zinc fingers of the Krüppel type, and at the N-terminus a Q/P-rich transregulatory domain, both characteristic of transcription factors. However, recent findings suggest that WT1 may also be involved in a post-transcriptional process. Specifically, WT1 isoforms containing the alternatively spliced exon 9 (+ KTS), preferentially associate with nuclear speckles and co-immunoprecipitate splicing antigens (1); furthermore, WT1 has been shown to interact with the ubiquitous splicing factor U2AF65 (2), and binds to RNA in vitro (3, 4). To extend these findings, we have fractionated nuclear extracts to see if particles containing WT1 have the properties of RNP. In summary, WT1 is enriched by oligo(dT) chromatography, as are U2AF65, the U5 snRNP associated protein p116, and hnRNP A1. Gel filtration and sedimentation profiles suggest that WT1 is present in RNase-sensitive particles, >2 MDa in size, peaking at ~60S, and ~1.27 g/cm3 on Nycodenz. Similar results were obtained from two cell lines expressing WT1, fetal kidneys (day E17), and transiently transfected cells, suggesting that the presence of WT1 protein in nuclear poly(A)+ RNP is a general aspect of WT1 function.