Expression of phytoglobin (Hb) was investigated in germinating barley embryos. Hb mRNA was detectable on northern blots within 2h of the start of imbibition and expression continued to increase up to radicle elongation. The amounts of mRNA expressed were decreased under an atmosphere of 40% O 2 and increased under 3% O 2 suggesting a link with low-oxygen stress in these embryos. When previously imbibed seeds were stored dry before the onset of radicle protrusion, the seeds remained viable for at least 1 year and Hb mRNA was detectable in the embryos throughout this time. However, under unfavourable storage conditions, Hb presence in the embryos correlated with poor viability in storage. These findings are discussed in relation to the use of Hb as a germination marker, its use as an indicator of quality loss and its importance in energy maintenance in the seed.