On certain natural transformations between connections Miroslav Doupovec and Alexandr Vondra Abstract. We determine all natural transformations of $J^1(J^1(Y\to X)\to Y)$ into $J^1(J^1(Y\to X)\to X)$ over the identity of $J^1(Y\to X)$. Then we interpret the analytical result geometrically and correlate it with the geometry of connections on $Y\to X$. Keywords. Natural operator, jet prolongation, connection. MS classification. 53C05, 58A20.