Seeds of Avena ludoviciana after-ripened more rapidly with increasing temperatures up to 30°C and with increasing relative humidities between 16 and 100%. In continuous light, these seeds after-ripened more rapidly than in the dark. Seeds of different species and strains of wild oats after-ripened at different rates; primary seeds after-ripened more rapidly than secondary. One week after anthesis 60% of the viable primary seeds of A. ludoviciana were dormant, compared with 100% at maturity. The importance of these findings to studies on the physiology of dormancy and to the control of wild oats in the field is discussed.