The report describes the activities and results from 1987 within the open sea programme of the national Swedish monitoring programme, PMK. The open sea programme also forms the major part of the Swedish contribution to the Baltic Monitoring Programme of the Helsinki Commission. Two regular oceanographic cruises were carried out to the Baltic, two plus one supplementary cruises to the Gulf of Bothnia, three in the Kattegat and five in the Sound. Several other cruises of relevance to PMK were also carried out. Standard oceanographic parameters including nutrients were analysed and various biological samples were taken including fish and mussel samples for analysis of harmful substances. From spring to autumn a negative temperature anomaly of 2-4°C was observed in the Kattegat and the Baltic. As in previous years the southern parts of the Kattegat showed very low oxygen values during a short period in the autumn, but the recovery was quick. Following the spring bloom the nutrient reservoir of the Baltic surface water was depleted to about 40 m until the early autumn. In the Gotland Deep the hydrogen sulphide has now resided for 10 continuous years in the deep water. During the last half of 1987 hydrogen sulphide appeared in the Bornholm Deep, extending into the Hanö Bight. Sulphide was present in the Landsort Deep for a short period.