A system of frequent small harvests combined with a regression technique is described, which evens out the flow of work in growth analysis experiments in controlled environments and thus makes it possible to deal with larger numbers of treatments than by the older method of large samples at long intervals. The method also reduces the amount of information ''at risk'' on any one harvest occasion. Regressions of the logarithms of total dry weight and of leaf area on time are fitted by computer. The progress curves of relative growth rates are obtained by differentiation of the regression equations and progress curves of unit leaf rate and leaf area ratio are also derived. The derived data obtained are in the form of smooth curves fitted over the whole growth period, instead of mean values for periods between pairs of sampling occasions. While best suited to experiments in controlled environments, this system is also applicable to many glasshouse and outdoor investigations.