Trends in structural and magnetic parameters are presented and discussed for Nd2Fe14−xTxB with T=Cr, Mn, Co, Ni, Al. Some data are also included on the Y analog systems. Partial Al substitution strongly increasesc/a. We show that this has to do with preferential occupation of the larger atom (Al) in the &sgr;Fe layer. Co and Ni substitutions increase Curie temperature (TC) while all others decrease it. Anisotropy constantsKfor 300 K decrease in all cases investigated compared to Nd2Fe14B. Some discussion is given to the general mode of preferential substitution and the concomitant effects on magnetic anisotropy.