Summary A high relative humidity treatment (HRH) stimulated frequency of root emergence and improved post-germinative growth and development from somatic embryos of sitka spruce (Picea sitchensis (Bong) Carr.). Comparison between temporal changes in embryo water content during the HRH treatment and its subsequent effects on germination revealed that, although the majority of water was lost during the first week of HRH treatment, gradual and significant improvements in germination were evident throughout a 5-week treatment period. Somatic embryos transferred directly from maturation conditions onto growth regulator-free medium showed rapid depletion of major storage proteins whereas those transferred to the HRH treatment (growth regulator-free and partial water loss) showed no loss in these proteins. Apparently, the partial drying prevented at least some metabolic events associated with early stages of germination. Longer periods of HRH treatment were required by embryos matured on 80 μM ABA to obtain germination equivalent to those embryos produced on 40 or 60 μM ABA, suggesting that there may be a relationship between endogenous ABA levels and the effects of the HRH treatment on germination. Extending the HRH treatment for longer periods increased the percentage of embryos that developed into high quality emblings (those exhibiting root emergence and an elongated, non-vitrified hypocotyl). ≪High quality emblings≫ acclimatized well to ex vitro conditions and, subsequently, developed into vigorous plants similar to typical sitka spruce seedlings.