A general model is presented to analyse size-dependent reproductive output in plants. The model formulation makes it possible to test for both a minimum size for reproduction and a non-linear relationship between size and reproductive output. The model, statistically analysed with the likelihood-ratio test, admits a hump-shaped relationship between reproductive effort (RE) and plant size. Data for Carlina vulgaris, Ipomopsis aggregata and Saxifraga hirculus show that RE is not always monotonically increasing or decreasing with plant size. -from Authors