This paper examines the relative importance of timing and persistence elements in explaining cyclical fluctuations in labor supply. Data from the natural experiment provided by World War I1 and cross-sectional data on American local labor markets, as well as aggregate time-series data are used in the empirical work. We find little evidence that timing effects play an important role in labor market dynamics. The evidence suggests that views emphasizing persistence are more accurate, and that previous employment tends to raise the probability of subsequent employment.