Northern blot analysis revealed that the histone H3 and H4 mRNAs are of unusual large size in germinating maize embryos. S1-mapping experiments show that the 3'-untranslated regions of the mRNAs transcribed from 3 H3 and 2 H4 maize genes previously described are much longer than in the non-polyadenylated histone mRNAs which represent a major class in animals. Moreover, oligo d(T) cellulose fractionation of RNAs isolated at different developmental stages indicates that more than 99% of the maize H3 and H4 mRNAs are polyadenylated. A putative polyadenylation signal is present in all five genes 17 to 27 nucleotides before the 3'-ends of the mRNAs.