It is a little hard to follow from your desription but I'm assuming you have 2 three dimensional curves that intersect.
So each curve is a set of points in 3-D space, where each point is given by an x,y and z coordinate value. Suppose you have m data points for each curve. Let the points in curve 1 be given by an m by 3 matrix, C1, where the first column is the x coordinate values, the second column is the y coordinate values, and the third column is the z coordinate values. Similarly let the points in the second curve be given by a m by 3 matrix C2 then you can use:
plot3(C1(:,1),C1(:,2),C1(:,3))
hold on
plot3(C2(:,1),C2(:,2), C2(:,3))
