We studied H1 gene expression in hybrids of Xenopus laevis (female) x Xenopus borealis (male) and saw paternal H1 synthesis in mid-blastulae, which indicates that the H1 genes are active by this stage. The behavior of the maternal store of H1 histone mRNA was studied in androgenetic haploids. In which all stored mRNA is of the laevis type and all new transcripts are borealis. This showed that the initial activation of H1 synthesis occurs entirely by mobilizing maternal transcripts and that these are then unstable, disappearing in a few hours, by the early gastrula stage.