Sex allocation theory predicts that growth rates should influence the optimal size at sex change, with sex change occurring at larger sizes with increasing growth rates. We examined how variation in food availability affects growth rates and therefore influences size at sex change in 2 protandrous calyptraeid gastropods, Crepidula cf. marginalis and C. incurva. The lowest food concentration tested resulted in starvation and was discarded. The medium and high food concentrations resulted in differences in growth rates, and in both species the penis was lost and sex change was initiated at larger sizes with more food. However, food concentration had little effect on the size at which the female stage was attained. Food-induced alterations in the timing of sex change were not in the expected direction. C. cf. marginalis raised with less food initiated sex change earlier, but completed sex change later in time than those raised with more food. C. incurva both initiated and completed sex change later when raised with less food compared to those individuals raised with more food. In both species the transitional phase was completed more rapidly with more food. These results are consistent with the idea that, as more resources become available, time dedicated to active sexual phases is maximized and the duration of the non-reproductive transitional phase is minimized. Under 'good' conditions this is manifest by a delay in the loss of the male phase, but no change in the attainment of the female phase.