Electrophoretic analysis of the most abundant subtype of histone H1 (H1-1) of 301 accessions of grasspea (Lathyrus sativus) and 575 accessions of lentil (Lens culinaris) revealed allelic variants which most probably arose due to recent mutations. In each species, a single heterozygote for a mutation was taken for construction of isogenic lines carrying different H1-1 variants. Sequencing of alleles encoding H1-1 in lentil, grasspea, pea and Lathyrus aphaca showed the presence of an extended region in C-terminal tail which we termed 'regular zone' (RZ). It consists of 14 6-amino-acid units of which 12 (pea and Lathyrus species) or 13 (lentil) are represented by an AKPAAK sequence. The structure of the hypervariable unit 8 is species-specific. At the DNA level most AKPAAK units differ in the third codon positions, implying the action of natural selection preserving the RZ organization. In lentil, the fast variant lost two units (including unit 8), while one AKPAAK repeat of the slow variant is transformed into an anomalous SMPAAK. The mutant variant of the grasspea H1-1 differs from the standard one by duplication of an 11-amino-acid segment in N-terminal tail. The isogenic lines of lentil and grasspea were compared for a number of quantitative traits, some of them showing small (1-8%) significant differences.