Non-programmers were asked to organize natural English commands of a laboratory programming language into programs for solving name-sorting problems. The problems differed in the sort concept to be programmed (conjunction vs. disjunction) and in the form of expression of the letter tests to be made on the names (affirmation vs. negation.) Programming performance was found to be impaired with disjunctive concepts and with letter tests involving negation. Different classes of program structure were identified and were associated with certain problem conditions and error measures. An influence of prior experience with procedures on performance was suggested. Program debugging and testing performance was characterized. © 1974, Academic Press Inc. (London) Ltd.. All rights reserved.