The effect of ethylene on quantitative and qualitative aspects of respiration in Spergula arvensis L. seeds was studied. Oxygen consumption and CO2 evolution from seeds increased 60 h after addition of ethylene to the dry seed; these increases were considered to be a function of the number of seeds that were germination, rather than a direct effect of ethylene. The respiratory quotient (RQ) on day 1 (0.5) was lower than on subsequent days, indicating an absence of anaerobic processes in the early stages of germination and the use of a different respiratory substrate to that oxidized on days 2–4. Measurements of C4/C1 ratios showed that ethylene did not break dormancy by initiating a switch from the Embden-Meyerhof-Parnas pathway (EMPP) to the pentose phosphate pathway (PPP). On the contrary, some evidence was obtained for a switch from the PPP to the EMPP after 3–6 h in pre-imbibed and non pre-imbibed seeds treated with ethylene.