Steel frames infilled with structural clay tile have been used in commercial and industrial buildings for most of this century. Often these buildings are located in moderate to high seismic zones and are likely to experience earthquake forces. Little prior research has been conducted to investigate the behavior of clay tile infills under lateral loading. Twenty-one large-scale clay tile infilled frames were tested to determine their behavior and correlate the results with other available experimental data. The infills greatly increased the in-plane stiffness and strength of the otherwise flexible framing. Two in-plane failure mechanisms were observed, diagonal cracking and comer crushing. Under uniform out-of-plane load, the infills cracked along the mortar joints and developed membrane forces. Tremendous out-of-plane capacity was observed as the panels arched vertically and then horizontally, remaining stable after ultimate capacity was reached. Under sequential and combined bidirectional loadings, the panels remained stable with little interaction of the in-plane and out-of-plane behavior, particularly in the frame member forces. Analytical comparisons of measured versus predicted stiffness, ultimate capacity, and frame member forces were performed. A numerical model based on a piecewise linear equivalent strut was developed. Recommendations for evaluation of clay tile infills subjected to seismic loads were …