Synopsis This paper describes in detail the, final results of a research programme started in 1964 to study the longterm characteristics of high alumina cement (HAC) concrete and reported briefly in a recent Building Research Establishment Information Paper. Current guidelines, for assessing the condition of buildings containing HAC concrete are discussed in the light of these and other laboratory results which have recently become availahle. The main conclusions relate to wet HAC concrete which is shown to continue reducing in strength even when highly converted and to reach lower minimum strength than concrete under dry conditions. This effect of wet storage is additional to the known vulnerability of HAC concrete, when wet, to chemical attack.