In recent years, a number of models of orthographic coding have been proposed in which the orthographic code consists of a set of units representing bigrams (open-bigram models). Three masked priming experiments were undertaken in an attempt to evaluate this idea: a conventional masked priming experiment, a sandwich priming experiment (Lupker & Davis, 2009) and an experiment involving a masked prime same-different task (Norris & Kinoshita, 2008). Three prime types were used, first-letter superset primes (e.g., wjudge-JUDGE), last-letter superset primes (e.g., judgew-JUDGE) and standard substitution-letter primes (e.g., juwge-JUDGE). In none of the experiments was there any evidence that the superset primes were more effective primes, the prediction made by open-bigram models. In fact, in the second and third experiments, first-letter superset primes were significantly worse primes than the other two prime types. These results provide no evidence for the existence of open-bigram units. They also suggest that prime-target mismatches at the first position produce orthographic codes that are less similar than mismatches at other positions. Implications for models of orthographic coding are discussed.