In this paper I present an empirical analysis of the dynamics of individual earnings using Spanish quarterly earnings. I propose a new econometric methodology to control for the seasonality in my dataset. Moreover, I apply this methodology to the study of earnings mobility in Spain, using transition probabilities among earnings quintiles for the period 1985-1996. I find substantial mobility from one year to the next. However, earnings changes are basically among adjacent quintiles. Workers with university education are more mobile than workers with primary and secondary education. On the other hand, I observe greater negative mobility among earnings quintiles and more persistence of low earnings situations over the nineties, and especially for workers with primary education.Keywords: lender of last resort, bank supervision, central banking, deposit insurance, incomplete contracts.