This report describes the activities and results from 1986 within the open sea programme of the national Swedish monitoring programme, PMK. The open sea programme also forms major part at the Swedish contribution to the Baltic Monitoring Programme of the Helsinki Commission. Two regular oceanographic cruises were carried out in the Baltic and the Gulf of Bothnia and three in the Kattegat. Several other cruises were carried out, which are relevant to the programme. Standard oceanographic parameters including nutrients were analysed and various biological samples were taken including fish and mussel samples for analysis af harmful substances. In September the surface water temperature decreased unusually in the Kattegat and the Baltic showing a negative anomaly at at least 2°C. As during previous years the southern part of the Kattegat showed very low oxygen values in the bottom water during a limited period in the autumn. In other respects the oceanographic conditions in the Kattegat area were normal, whereas in the Eastern Baltic bad oxygen conditions with hydrogen sulphide prevailed in the bottom water for the nineth year. In the southern Baltic and west af Gotland hydrogen sulphide was found in the bottom water only during the first half of the year.