Needle water potential (Ψ n), stomatal resistance ( r s) and net photosynthesis ( P N) were measured in potted radiata pine seedlings from three families (A, B, and C) during a soil drying and rewritting event. Measurements were made in a controlled environment of 25°C, 14-h days and 18°C, 10-h nights; vapour pressure deficit of 16 mbar; photon flux of 400 μE m −2 s −1; and wind speed of 1 m s −1. Stomatal resistance increased at a greater rate in family A than in family B than in family C as Ψ n decreased during the drying phase: at −25 bar Ψ n, r s values were 77, 60, and 46 s cm −1 for families A, B and C respectively. Net photosynthesis ( P N) was greatest in family A at high Ψ n but least at low Ψ n: at Ψ n −9 bar, P N was 9.4 6.4, and 8.2 ng cm −2 s −1 for families A, B, and C respectively, but for −25 bar Ψ n corresponding P N values were 0.4, 1.1, and 0.9. Consequently family A had a greater proportional decrease in both P N and water use efficiency from high Ψ n to low Ψ n. This may help explain in part observed field behaviour (P.P. Cotterill, unpublished) where family A produces well relative to other families when weeds are controlled (high Ψ n condition) but produces less well relative to other families when weeds are not controlled (low Ψ n condition). Recovery of Ψ n after rewatering preceded that of r s and P N, and recovery of P n was typically biphasic with 70% of recovery coinciding with recovery in Ψ n and the remaining 30% more closely coinciding with recovery in r s. Recovery was slower in family A than the other two families.