Speech error span has been investigated in 988 phonological, morphological (root and affix) and lexical errors. Exchanges, interrupted anticipations, uninterrupted anticipations and perseverations were analyzed in an Italian corpus of 2500 manually recorded speech errors. Phonological, morphological and lexical levels were compared. Span was computed in term of number of phonemes existing between the error and its origin. A gradient in the span has been found between lexical, morphological, and phonological levels, the former being the longer. Affix errors have a longer "span" than root errors. Exchanges and interrupted anticipations have a longer "span" than both uninterrupted anticipations and perseverations. Results are consistent with a modular model of word production. Lexical level must be separated from phonological level and also from morphological level. Morphological level should be divided into affix and root sublevels.