This study examined the relationship between knowledge of sequence relations and the process of mental rotation in four-year-olds. Subjects were 12 preschool children who were tested individually. They were given a State Comparison Task (SCT) in which they were shown pairs of animal pictures, half identical and half mirror images of one another, and asked to decide if the figures were the same or different. The Sequential Ordering Task (SOT) involved showing animal shapes rotated from zero to 180 degrees in increments of 45 degrees. Children were shown either the first or last card of the sequence and the remaining 4 cards in random order; their task was to place the cards in the correct sequence showing a rotation from upright to 180 degrees. Responses were timed to one-thousandth of a second. Findings indicated that there was a significant positive correlation between the number of correctly placed cards in the SOT and the number of correct trials in the SCT. Some four-year-olds understood sequence relations; most performed at better than chance levels on the SOT. Some four-year-olds used mental rotation. However, Rotators did not perform the SCT better or more quickly than did Non-Rotators, suggesting that mental rotation was not essential to this task. (KDFB)