Endopolygalacturonase [poly (1–4‐α‐D galacturonide) glycanhydrolase, EC 3.2.1.15] activity was measured in samples of cv. Rutgers, Nr (never ripe) and F1hybrids of rin (ripening inhibitor, + rin, ++), nor (nonripening, ++, + nor) and rin × nor (+ rin + nor) fruits taken at three day intervals during ripening. Day 1 of ripening was taken as the day on which the first persistent increase in ethylene production was recorded. The enzyme was first detected on day 3 in Rutgers, F1rin and F1nor, and on day 6 in Nr and F1rin × nor. The Rutgers and F1rin samples softened more rapidly than the other samples and they also contained more enzyme activity. Enzyme activity developed less rapidly in Nr than in any other samples, but the Nr and the nor hybrid, samples softened at comparable rates. In Rutgers and F1rin, a high molecular weight form of the enzyme (PG1, Mr 100 000) predominated to day 6, and a lower molecular weight form (PG2, Mr 43 000 ‐ 46 000) progressively increased after day 6. In all F1nor, F1rin × nor and Nr samples the enzyme was predominately or entirely as PG1. The interrelationship of PG1 and PG2 and their roles in ripening ar