We develop a theory of differential equations associated to families of
algebraic cycles in higher Chow groups (i.e., motivic cohomology groups). This
formalism is related to inhomogeneous Picard--Fuchs type differential
equations. For families of K3 surfaces the corresponding non-linear ODE turns
out to be symilar to Chazy's equation.Comment: 8 pages. Final version. To be published in Annales de l'Institute
Fourie