Twenty-eight seed lots of two onion cultivars (Diana F1 and Aki) were created by naturally aging seeds during storage at 10% MC and 5 degrees and 25 degrees C for up to 22 months to investigate the ability of the vigour tests to identify differences in the extent of seed aging and possibly vigour. All seed samples were subjected to the following tests: standard germination test, cool germination test, electrical conductivity (E.C.), sugar and amino acid leakage from seed. Germination declined after more prolonged ageing in Diana, but remained high in Aki. E.C., sugar and amino acid contents in the seed leachate increased in both cultivars even when germination remained high, indicating a decline in seed vigour. The E.C. and sugar leakage from seed samples were highly correlated with performance in the stress conditions of the. cool germination test (r=-0.911; r=-0.808, respectively). Leakage tests therefore appear to be suitable for evaluating seed quality in onion seeds and could be further developed as a rapid vigour test.