This paper describes a series of tests carried out on large diameter (greater than 300mm) GFRP tubes filled with concrete. The test programme complemented and extended an existing test programme being carried out by Southampton University. Both eccentrically and axially loaded specimens were tested with aspect (height to diameter) ratios ranging from 2:1 to 10:1. Failure of all the axially loaded specimens occurred by fracture of the GFRP near the centre of the column. For the specimens tested the GFRP was found to increase the compressive strength of the concrete in the columns by a factor of 3. Existing theoretical models were found to give reasonable predictions for the enhancement in strengths of concrete when account was taken of the confinement efficiency. All of the eccentrically-loaded specimens were observed to fail by breaking in half at or near mid-height. A method of predicting the failure load of the eccentrically loaded columns was developed and found to give reasonable predictions (ranging from 80 to 111%) of the measured values. Dr. R. M. Moss, BSc, PhD, CEng, MIStructE Centre for Concrete Construction, BRE