A set of procedures for testing hypotheses about the syntactic structure of natural languages has been developed for use on-line with computer display consoles. The procedures were designed in the context of Chomsky's transformational generative grammar. A linguist can construct phrase structure trees, selecting with the lightgun from alternative expansions shown on the display scope. When a base tree has been generated, transformational rules can be applied to it. The deep structure of a sentence can be determined using the logic of the MITRE Syntactic Analyses Procedures. Phrase structure and transformational rules can be changed, rearranged, regrouped, and tested. (Author/FWB)