The results of cyclic loading tests on three full-size portal frame knee joints are presented. All members complied with the flange and web slenderness limits for plastic design (AS 1250-1981) but were the lightest sections for their respective depths. Large decreases in load capacity were observed when either lateral-torsional or combined local flange and web buckling occurred. Lateral restraint forces were measured and were found to exceed the minimum ultimate strength values specified by the design code rules. One fully welded connection and two bolted connections were used and suffered only minor damage during the tests.