This paper is concerned with derivations in algebras of (unbounded) operators affiliated with a von Neumann algebra $\mathcal{ M}$. Let $\mathcal{ % A}$ be one of the algebras of measurable operators, locally measurable operators or, $\tau $-measurable operators. We present a complete description of von Neumann algebras $\mathcal{ M}$ of type $I$ in terms of their central projections such that every derivation in $\mathcal{ A}$ is inner. It is also shown that every derivation in the algebra $LS(\mathcal{ M})$ of all locally measurable operators with respect to a properly infinite von Neumann algebra $\mathcal{ M}$ vanishes on the center of $LS(\mathcal{ M})$.
Categories: math.OA math.FA