This research project estimated migrant and seasonal agricultural workers in four Midwestern States in 1988, using the Public Health Service's definitions of such workers. Researchers collected federal agricultural data and state reports on migrant education programs and crop patterns, and considered other potential data sources. Numerous methodological difficulties led to the decision to consult a network of knowledgeable persons in each state. These people provided data on numbers of workers and dependents, counties involved, crops, length of season, peak times, worker origins, worker ethnicity, and proportion of workers traveling with families. Comparisons of data from all sources produced estimates indicating the number of migrant workers and dependents in each county during a specified peak month. State totals of maximum estimated peak numbers of migrants and dependents are: workers 925, dependents 815 for Iowa; workers 2,890, dependents 3,070 for Kansas; workers 910, dependents 555 for Missouri; and workers 3,250, dependents 1,310 for Nebraska. Most migrants were Hispanics with a home base in Texas. Estimates for seasonal workers were based primarily on the 1978 and 1982 Censuses of Agriculture, and are believed to be similar to 1988 figures. Estimated totals of seasonal workers and estimated maximum number of dependents for each state in 1982 are, respectively, 14,805 and 21,275 for Iowa; 5,949 and 8,549 for Kansas; 8,637 and 12,411 for Missouri; and 6,701 and 9,629 for Nebraska. The size of the migrant and seasonal workforce is expected to remain stable for the next 5-10 years. This report contains 14 tables and maps, lists of data sources and contacts, a set of official definitions, and the survey questionnaire. (SV)