A survey of 224 Michigan citizens called for jury duty over a 2-month period was conducted to assess the jurors' comprehension of the law they had been given in the judges' instructions. Citizens who served as jurors were compared with a base line of those who were called for duty but not selected to serve, and with those who served on different kinds of cases. Consistent with previous studies of mock jurors, this study found that actual jurors understand fewer than half of the instructions they receive at trial. Subjects who received judges' instructions performed significantly better than uninstructed subjects on questions about the procedural law, but no better on questions about the substantive (criminal) law. Additionally, jurors who asked for help from the judge understood the instructions better than other jurors. Since the results replicate previous research using simulated trials, this study provides evidence for the generalizability of earlier work to actual trials.