The coefficients of linear expansion alpha for silver, copper and aluminium are determined by a sensitive method and compared with those of other workers. The reduced parameters alpha /( alpha )_m/2 and T/T_m give a common curve for all metals. Here T_m is the melting point and ( alpha )_m/2 is the value of alpha at T=¹/₂T_m. The curve is a straight line within the approximate limits 0.2<T/T_m<0.45 and is found to deviate considerably from linearity at higher temperatures. Assuming that the deviation is due to defects, the energies of monovacancy formation in close-packed cubic metals are estimated and are found to agree excellently with the observed values.