The effect of sulphur deprivation and irradiance (180 and 750 µmol m-2 s-1) on plant growth and enzyme activities of carbon, nitrogen, and sulphur metabolism were studied in maize (Zea mays L. Pioneer cv. Latina) plants over a 15-d-period of growth. Increase in irradiance resulted in an enhancement of several enzyme activities and generally accelerated the development of S deficiency. ATP sulphurylase (ATPs; EC 2.7.7.4) and o-acetylserine sulphydrylase (OASs; EC 4.2.99.8) showed a particular and different pattern as both enzymes exhibited maximum activity after 10 d from the beginning of deprivation period. Hence in maize leaves the enzymes of C, N, and S metabolism were differently regulated during the leaf development by irradiance and sulphur starvation. and S. Astolfi, M. G. de Biasi, C. Passera.