Different models of spoken word production make different predictions regarding the extent of effects of certain word properties on the output of that model. These predictions are examined with regard to the effect of these variables on the production of semantic and phonological errors by aphasic subjects. Thus the production of semantic errors is found to be affected by imageability and the production of phonological errors by word length, but not vice versa. It is argued that this pattern of variables affecting the production of semantic and phonological errors is better explained by models which require strictly sequential stage-by-stage processing (e.g. Levelt et al., 1991a; Morton, 1970; 1979) than by multi-layer perceptron (e.g. Plaut & Shallice, 1991; 1993) or interactive activation models (e.g. Dell, 1986; 1989).