Ordered and disordered intergrowth structures between perovskite and NbO type elements in the K-, Sr- and Ba-Nb-O systems have been studied by means of electron microscopy and X-ray powder diffraction techniques. The ordered structures KNb4O6 and A(II)2Nb5O9 (A(I)= K and A (II) = Sr, Ba) consist of lamellar intergrowths of A(I, II)NbO3 and NbO slabs, the latter being one unit cell thick. In the A (II)-Nb-O systems a two dimensional intergrowth between A(I, II)NbO3 and NbO blocks of varying sizes also exist, in a phasoid region called 03B1. Combined HREM studies and EDS-analysis of the Ba-analogue of the 03B1-phasoid gives the approximate composition ~ BaNb4O6. In the HREM images one can also find small domains of more ordered intergrowth. These are discussed in terms of micro-phases and homologous series. Some factors influencing the block sizes in the structure are also discussed.