During a stay in Surinam (I February-15 April, 1989) I conducted research on a running water system'in the tropical rain forest, tOO km SW of Paramaribo (5°48'N, 55°85'W). I visited the Siparikreek and the Tibitiriver for 14 days. Although it was supposed to be "the short dry season”, from February to April, it rained in the afternoon nearly every day. On 18 February I observed dragonflies near the Siparikreek, 50 m downstream from the bridge connecting Zanderij and Witagron. Most Odonata disappeared as heavy rainfall started around 14.25 h. A few minutes later I noticed a zygopteran flying low over the water surface, with its abdomen slightly pointed down, at an angle of about 10 degrees. It turned out to be a patrolling male of Oxystigma williamsoni Geijskes. Other males were perching on the shore vegetation at a height of 5-10 cm. Soon after this, a female was seen ovipositing alone in a floating leaf. The male grasped her and they flew in tandem into the forest. Between 14.44 and 14.48 h four couples arrived at the site where the first female had been seen ovipositing. During oviposition, the pairs maintained the tandem position. When rainfall decreased around 14.55, single patrolling males disappeared. But when a few minutes later the rain increased, they were again seen flying low over the water or perching on shore vegetation. At 15.00 1 had to leave the site.