To analyze the organization of spliceosomal snRNPs in plant nuclei, we have used both immunofluorescence labelling with the antibody 4G3, raised against the human snRNP-specific protein U2B", and in situ hybridization with anti-sense probes to conserved regions of U1, U2 and U6 snRNAs. The organization comprises a fibrous interchromatin network, which may include both interchromatin fibrils and granules, and very prominent nuclear and nucleolar-associated bodies. Double labelling with an anti-p80 coilin antibody shows that these are coiled bodies. Dynamic changes in the labelling pattern were observed through the cell cycle, and in response to and on recovery from heat shock. The similarity of this organization to that observed in mammalian nuclei is strong evidence that it is fundamental to the processing of pre-mRNA in eucaryotes in general.