This paper describes two experiments using a masked priming method with 60 ms SOA. In the first experiment, the task was an alphabetical decision. The stimuli were isolated letters or non-alphabetical symbols, preceded by a similar or different prime, while the primes were scaled down or 180° rotated. Response times to letters revealed priming effects for both prime transformations. In the second experiment, the task was a lexical decision, and the stimuli were five lower-case letter words or pseudo-words. The priming conditions were similar to those of the first experiment. Response times to words revealed priming effects for both prime transformations, however the priming effect was only marginally significant for rotated primes and it appeared dependent on the frequency of use of the prime. A significant correlation between priming effects and the frequency of use of the different prime words was observed. We concluded that scale invariant features are used in the perception of letters and words as well, while 180° rotation invariant features are used in the perception of letters, but no such a conclusion can be drawn for words, in general.