GRIDXY(X) plots vertical grid lines at the positions specified by X. GRIDXY(X,Y) also plots horizontal grid lines at the positions specified by Y. GRIDXY(..., 'Prop1','Val1','Prop2','Val2', ...) uses the properties and values specified for color, linestyle, etc.
Examples:
plot(10*rand(100,1), 10*rand(100,1),'bo') ; % random points
gridxy([1.1 3.2 4.5],'Color','r','Linestyle',':') ; % horizontal red dashed grid
h = gridxy([],[2.1:0.7:5 8],'Color',[0.9 1.0 0.2],'linewidth',3) ; % vertical solid thicker yellowish grid, and store the handle

GRIDXY can be used to plot a irregular grid on the axes.