Development of two annual medics (Medicago scutellata cv. Robinson and M. truncatula cv. Jemalong) was recorded under four controlled day/night temperature regimes of 12/5°, 18/11°, 24/17° and 30/23°C. Equations expressing the fractional daily increments of development as a function of daily mean temperatures were derived from the results. From these equations and field temperature data, predictions of development in the field were compared with observations from 24 serial monthly plantings at Warwick in southern Queensland. Predictions were satisfactory for all stages from planting to first mature pod for cv. Robinson and for all stages except flowering for cv. Jemalong. Inclusion of a vernalization constraint with daily minimum temperatures improved the prediction of flowering, but unknown factors delayed this stage in plantings of cv. Jemalong from January to April.