This paper describes results of an experimental program conducted to determine the influence of deep side-grooves on fatigue crack retardation. The results indicate that side-grooves significantly reduce the delay in fatigue crack growth caused by single peak overloads. It is suggested that the decreased retardation is due to simulation of plane strain conditions in the "thin" test sections by the stress field at the root of the side-groove. NOMENCLATURE a = crack length B = specimen thickness B, = net thickness after side-grooving B = stress intensity factor coefficient da/dN = fatigue crack growth rate cXSC = u-component of strain in side-grooved specimen cXUT = x-component of strain in uniform thickness specimen AK = stress intensity factor range during load cycle K,,, = maximum stress intensity factor during load cycle Kpeak = peak stress intensity factor during overload K,,,, = actual stress intensity factor for side-groove specimen K * = stress intensity factor computed for side-groove specimen assuming uniform thickness B, N , = delay cycles caused by overload 11 = empirical exponent P = applied force R = minimum/maximum load (J = root radius of side-groove notch 0 = side-groove flank angle W = specimen width.