A laboratory flask is designed for the growth of tissue, cells or microorganisms in a culture medium. The flask includes a bottom wall which accommodates the culture medium. The interior of the flask is accessible from an opening in a side wall through a neck extending outwardly therefrom. The neck of the flask is raised above an upper planar surface of the flask, so as to maximize the height between the neck and the bottom wall, thereby permitting an increase in the usable volume of the flask. The inner wall of the neck includes a depending filler wall extending between the inner wall of the neck and the upper planar surface of the flask to fill a gap which would otherwise exist therebetween. The flask permits accommodation of a standard screw-threaded cap to close the neck.