Concurrent measurements of steady-state accommodation response/stimulus curves and of pupil diameter were made in groups (n = 20) of young, adult myopes [age (mean +/- SD) 23.1 +/- 4.5 years, mean-sphere error (MSE) -3.06 +/- 2.35 D, range -0.60 to -8.54 D] and emmetropes (mean age 25.3 +/- 5.7 years, mean MSE -0.07 +/- 0.26 D, range -0.50 to +0.50 D). The aim of this study was to explore the possibilities that pupil diameters with relaxed accommodation were larger, and that accommodative miosis was weaker, in the myopic group. Such behaviour would lead to relatively greater degradation of the retinal images in the myopic group, even though aberrations at constant pupil diameter and dioptric accommodative lags in the two groups were the same: this might result in excessive axial growth and further myopia development. No evidence for any systematic refractive dependence of pupillary characteristics or accommodative responses was found. Interestingly, those subjects whose response/stimulus curves had a higher slope tended to display greater accommodative miosis, irrespective of their refractive error.