Spontaneous language samples are a useful tool in studying the nature of morphosyntactic production in both clinical and academic settings. However, little work has been done on typical frequency of occurrence of morpheme production and even less on the degree of temporal reliability of morpheme frequency between samples. This study compares two language samples recorded within a week of each other under similar conditions in a test-retest paradigm for each of 23 typically developing children aged 2;6-3;6 to examine the production of the following morphemes associated with specific language impairment: contracted auxiliary, copula, do as an uncontracted auxiliary, be as an uncontracted auxiliary, third person singular and past tense. Also analyzed were all utterances containing more than one verb. Frequency and reliability of four different sample lengths ranging from 50 to 200 utterances were tested. Results showed generally low degrees of reliability at 50 and 100 utterances, with only limited improvement for most targets at 200 utterances. Clinical implications of these results are discussed. (Contains 4 tables.)