Field experiments were conducted on pickling cucumbers (‘M-27’) to determine the ontogenetic relationships between seed dry weight, carbohydrate composition and fruit size as influenced by the cultural environment. In 1990, 360 fruit varying from 1.8 to 8 cm in diameter were harvested and the dry weight of 35 seeds randomly extracted from each fruit was measured. The 1991 experiment consisted of four planting times (4 and 17 June, 1 and 17 July) as treatments. Expansive fruit growth rate was measured and 20 seeds per fruit were extracted from fruit ranging in diameter from 4.0 to 5.8 cm. Mean seed dry weight (DW) increased in an exponential manner relative to fruit diameter, attaining a DW of over 10 mg in 7 cm diameter fruit. Environmental conditions in the separate plantings, during the period of reproductive development, affected the rate of fruit growth, as well as mean seed DW in 4.0 and 5.0 cm diameter fruit. The concentrations of sucrose, fructose and glucose in seed tissue were high early in embryogenesis (200 mg, 140 mg and 70 mg g −1 DW respectively), but declined to relatively low levels (60 mg, 37 mg and 14 mg g −1 DW) by the time the seed had reached approximately 2.5 mg per seed DW.