This report describes the porewater investigation carried out on drillcore material from deep boreholes within the Laxemar Site Investigation programme. Porewater residing in the low-permeability matrix of a rock body cannot be sampled by conventional groundwater sampling techniques, but has to be characterised by indirect methods based on drillcore material. Such determination might be subjected to various types of induced perturbations, which need to be understood for the interpretation of the data at in situ conditions. Once the produced data can be judged to reliably represent in situ conditions, they might be used for the characterisation of the exchange between porewater and fracture groundwater and, based on quantitative models, help to establish the conceptual model of the palaeohydogeological evolution of the site during Holocene and Pleistocene times. At the Laxemar and Forsmark sites, porewater investigations based on various diffusion experiments utilising fresh drillcore material have been conducted for the first time in crystalline rocks. This required a rigorous control of the acquired data and supporting experiments in order to understand possible perturbation effects such as stress releases, the drilling process, and by sample de-saturation. The present report presents applied methods and their uncertainties, the chemical and isotopic porewater data generated from the raw data, model attempts for the in situ porewater composition, transport properties of the rock, and implications of the porewater geochemistry on the palaeohydrogeological evolution of the Laxemar site. To interpret the porewater data, special emphasis is given to the integration of geological, hydrogeochemical, hydrological and palaeoclimate data from the overall Laxemar site descriptive model and, when appropriate, vice versa.