The chromosomes of a field bean line with a reconstructed karyotype (ACB) were hybridized in situ with biotinylated probes of a repetitive Fok I sequence, of DOP-PCR (degenerate oligonucleotide primed polymerase chain reaction) amplified DNA from a chromosome that does not contain this sequence, and with probes containing dispersed repetitive sequences. The results were compared with Giemsa banding, DNA late replication and Fok I in situ digestion patterns. This allowed further differentiation between the chromatin types of this species. Centromeric and NOR-associated heterochromatin as well as euchromatin were shown to be free of Fok I sequence repeats. Among the interstitial late replicating Giemsa bands, subdivided into 'marker' and 'additional' bands, most of the marker bands located at mid-arm positions were composed mainly or exclusively of tandemly arranged Fok I repeats. Some of the marker bands and nearly all of the additional bands located in the vicinity of centromeres were free of FokI sequence repeats, of Fok I recognition sites, and possibly also of dispersed repetitive sequences. They are probably composed of specific, not yet defined, repetitive sequences.