Abstract In maturation cultures, non-plasmolysing moisture stress induced by polyethylene glycol (PEG) 4000 reduced white spruce embryogenic tissue proliferation and stimulated somatic embryo development. Levels of endogenous putrescine (Put), spermidine (Spd) and spermine (Spm) in the cultures were quantified by high performance liquid chromatography (HPLC). In the cultures, free and conjugated Spd were predominant. Compared with no PEG treatment, levels of free polyamines (PAs) were lower in PEG treatments at days 5 and 10 in the cultures but increased to higher levels thereafter. Although the levels of conjugated polyamine increased early during somatic embryo maturation, the changes of conjugated polyamine levels were similar to those of free PAs. Throughout the maturation process, levels of bound Put and bound Spd in PEG treatments were lower than those in the controls. The level of bound Spm was higher in PEG treatments at day 5, it declined then to a lower level thereafter. Methylglyoxal bis(guanylhydrazone) (MGBG) decreased the levels of endogenous free PAs and reduced tissue growth in the cultures with or without PEG treatment. However MGBG did not inhibit embryo development in these cultures. In 0.2 mM MGBG treatments, although the number of cotyledonary embryos increased on the basis of fresh weight of tissue, the number per dish decreased. In PEG treatments, the maximum concentration which tissue could tolerate was lower than that in the cultures without PEG. Thus, reducing tissue proliferation by PEG may be due to inhibition of endogenous PA levels. However, the stimulation of embryo development by PEG may not solely function through the change of endogenous PA levels as MGBG did not stimulate or inhibit embryo development.