A flugate gradiometer survey was undertaken of accessible areas within the grounds of Severalls Hospital, Colchester, in advance of trial-trenched evaluation. Much of the site is occupied by buildings, roads, paved areas and woodland, and was unsuitable for geophysical investigation (out of the total site area of 41.6 ha, only 9.1 ha. was suitable, mainly around the periphery of the hospital site). The magnetometer readings were collected along transects 1m apart using Bartington 1m fluxgate gradiometers, and are plotted at 25cm intervals along each transect.<1> The survey detected numerous ground disturbances relating to the presence of the hospital and the modern history of the site, but also identified a number of relatively undisturbed areas of ground where there is at least the potential that archaeological sites or features might have survived. Most of the areas investigated in the northern half of the site (areas 1-5), as well as 7-9 in the south-west fall within this category. Much of the ground in the south-east of the site (areas 10-12) is heavily disturbed, or contains dense scatters of recent debris. Specific findings identifiable in the survey plots include ditch-like features (A, B, D, E, G, H) in areas 2-4 and 8-9. These could be drains or trenches of recent origin, but the possibility that some could predate the hospital cannot be entirely excluded. Strong linear features at F and J (in areas 3 and 12) do not appear to ferrous pipes. It is not impossible they could indicate near-surface tunnels, but it is probably more likely that they represent nonferrous pipes, or metalled paths or tracks.