Response spectra and spectrum intensity for the vertical component of strong motions recorded at El Centro (1940), Olympia (1949) and Taft (1952) are evaluated. Comparison with results for horizontal ground motion components indicates: (1) spectrum intensity of vertical components is about 20 to 30 per cent of that for horizontal components, and (2) spectra for vertical components are relatively accentuated in the shorter-period range and reduced in the longer-period range. Results of analysis of a typical earth dam cross-section subjected separately to two (N69W and vertical) components of Taft ground motion are presented. The two dimensional stress analysis technique used is based on the finite element concept. The significance of response to vertical ground motion is discussed. It is concluded that effects of vertical component of ground motion are large enough to warrant consideration for this class of structures.