The effect of the plant growth regulator PGR-IV on cotton (Gossypium hirsutum) was evaluated in field experiments in up to eight locations, for three years (1995-97) in Greece. Seedcotton yields were increased by up to 20 % in most locations, compared to the control. The mean yield increase in all locations and years was 4.9%. This was correlated with increases in boll retention, number of sympodia with two bolls and total boll number per plant. Late PGR-IV applications had no significant effect on seedcotton yield, compared to the PGR-IV treatment with three applications. No effect was found in plant height and fiber quality parameters. It is concluded that PGR-IV can increase seedcotton yield by affecting plant performance.