Data are presented relating various stages of growth of field-grown bush tomatoes cv. Sleaford Abundance established from dry and pre-germinated seeds and from transplants to accumulated day-degrees. In general, Ontario units predicted the dates of 50% flowering, of the first harvest and the date when 37·5 t/ha of ripe fruit had been picked, more accurately than day-degrees above 10 °C or calendar days. The number of Ontario units from sowing to 50% flowering for dry and pre-germinated seeds were 956 ± 35 and 871 ± 85, respectively. The corresponding figures from sowing to first harvest were 1958 ± 59 and 1867 ± 85. For transplanted crops the number of Ontario units from planting to 50 % flowering and from planting to first harvest were 322 ± 62 and 1352 ± 133, respectively. For transplanted crops the number of Ontario units required to give a yield of ripe fruit of 37·5 t/ha (the minimum level currently necessary on economic grounds for tomatoes for processing) was 1937 ± 112. Using this figure in conjunction with long-term meteorological records it was estimated that crops established from transplants at East Mailing, Kent (latitude 51° N), would fail to give yields of ripe fruit of 37·5 t/ha by late September on only 1–6 occasions in 100 whereas at Wellesbourne, Warwickshire (52° N) and Warsop, Nottinghamshire (53° N) crops would fail to reach this yield on 13–53 occasions in 100. Crops established directly from seeds would fail to give this yield on more than 50 occasions in 100 at all three sites.