Ratcliff, Clark. and Shiffrin (1990) examined the list-strength effect: the effect of strengthening (or weakening) some list items upon memory for other list items. The list-strength effect was missing or negative in recognition, missing or positive in cued recall, and large and positive in free recall. We show that a large number of current models fail to predict these findings. A variant of the SAM model of Gillund and Shiffrin (1984), involving a differentiation hypothesis, can handle the data. A variant of MINERVA 2 (Hintzman, 1986, 1988) comes close but has some problems. Successful variants of a variety of composite and network models were not found (e.g., Ackley, Hinton, & Sejnowski, 1985; Anderson, 1972. 1973; Metcalfe Eich, 1982; Murdock, 1982; Pike. 1984). The results suggest constraints on the future development of such models.