A study examines differences in lexical processing in first and second languages through error patterns in speech. The investigation assumes that although the internal planning of speech cannot be examined, it is manifested in output errors, such as slips of the tongue, writing errors, aphasic speech, and some temporal properties of speech, and can be elicited in responses to some psycholinguistic tests. An examination of errors in the first and second language processing of Finnish speakers suggests that lexical errors are different in the two languages. It is concluded that errors reflect individual stress and various situational and interactional factors, and that these factors deserve more attention in the study of speech. (MSE)