Several methodological issues related to second language acquisition research are considered, and a two-part study is discussed that addresses issues related to data collection, i.e., how and how frequent, and data analysis, i.e., the appropriateness of the statistical tools, the justification of inferences and the comparability of results based on different methods. The study, part of a larger 10-month longitudinal investigation of sequences in second language acquisition, sought to answer two major questions: whether the morpheme order obtained using an elicitation instrument (the Bilingual Syntax Measure) resembles the order of morphemes obtained from spontaneously collected second language acquisition speech data, and whether the cross-sectional and longitudinal research findings in second language acquisition research are comparable. In part on of the study, a one-hour taped speech protocol for each of six untutored Spanish speakers learning English was examined. In the second part of the study, the cross-sectional order of one of the subjects was compared with his order of morpheme acquisition once a month over the ten months of the study. A great deal of variability was found in the data, and the findings raise serious questions about the validity of cross-sectional studies of second language acquisition, at least in the area of morpheme acquisition. (SW)