An "intelligent" system for constructing computer-assisted pattern drills to be used in second language instruction is proposed. First, some of the difficulties in designing intelligent error analysis are discussed briefly. Two major approaches to error analysis in computer-assisted instruction, pattern matching and parsing, are described, and their advantages and disadvantages are examined. A third approach that appears to minimize technical problems is then outlined. This approach is based on the idea that a limited list of randomly generated sentences in the target language is useful in constructing transformation or pattern drills. The system consists of four parts including: (1) a module in which sentence templates can be constructed; (2) a procedure for transforming linguistic material into target language sentences; (3) stimulus sentence creation, including student response; and (4) error analysis, providing feedback to both the student and the sentence-generating system and allowing tailoring of further stimulus sentences. Some problems of implementation are discussed, including system response speed, feasibility of expansion beyond simple sentences, generation of inappropriate sentences, and constraints imposed by left-to-right template construction, transformation, and response judging. (MSE)