A study has been made to identify the contribution of senescent changes occurring in embryonic and non‐embryonic (endosperm and aleurone layer) tissues on germination of wheat (Triticum durum L. cv. Appulo) seed lots of 97, 93 and 70% viability. Measurements of germination and rates of macromolecular synthesis of embryos excised from dry seeds showed that as seed viability declined from 97 to ca 93%, there was a decrease in the capacity of embryos to grow and synthesise protein, RNA and DNA. However, no significant differences were observed between embryos from 93 and 70% viability seed stocks. Changes in nutrients, fresh and dry weights of embryonic and non‐embryonic tissues and electrophoretic patterns of endosperm proteins by sodium dodecyl‐sulfate polyacrylamide gel electrophoresis showed a reduced mobilisation of reserve material in 70%‐viable seeds. α‐Amylase (EC 3.2.1.1) production was also decreased. It is suggested that alterations occurring in non‐embryonic structures play a significant role in seed viability loss. This role might be mediated by failing nutrient supply, but the involvement of some inhibitor or toxic substance is also possible.