This paper reports on a preliminary quantitative study of syntactic constraints on code-switching within discourses in which no change in participants, setting or topic is evident. The goals of the study are to provide a syntactic description of the points at which switches from Spanish to English and English to Spanish are possible and to assess the extent to which actual behavior conforms to stereotypes represented by acceptability judgements. Use of the quantificational technique of accountable reporting of relative frequencies permits investigation of a wide range of questions, including (1) Do implicational relations exist among syntactic environments such that it can be predicted that a speaker for whom a switch in environment A is possible may also switch in environment B, but not vice-versa? and (2) Are the constraints on code-switching uniform throughout all populations and in all social situations or are there differences in frequencies and/or implicational hierarchies? The data consist of taped conversations of adults and adolescents collected by bilingual participant-observers in the San Joaquin Valley of California and in South-central Texas. Preliminary findings indicate that differences between speakers are variable rather than categorical but that implicational relationships do exist and that these are related to social phenomena. (Author/CLK)