Dissolved metals are generally considered the most mobile, toxic and bioavailable form of metals. However, the partition between dissolved and particulate phases is conventionally defined by the fraction passing through a 0.45 μm membrane, even though it is widely known that this fraction also includes different types of organic and inorganic colloids. Further size fractionation of metals in the dissolved phase can be performed using different techniques. The knowledge on the metal fractionation in stormwater is useful for assessments of the metals’ bioavailability as well as the performance of stormwater treatment systems. In this study, the size fractionation of dissolved metals in stormwater from four different urban areas in the city of Umeå, Sweden, is determined using ultrafiltration. The objective is to find a pattern for the size fractionation of different metals in the dissolved phase in stormwater and, by this, estimate the bioavailability of the metals. The investigated catchment areas include a parking space, a highway and two different commercial sites. The sampling campaigns will take place in the spring of 2016, taking samples from the stormwater drainage system using automatic samplers.