Here's an example that I think is similar to what you're trying to do. It sounds like you're using GUIDE, in which case use the handles structure to access the handles of the appropriate uicontrol objects. But the key is using get to query the value of one menu that was chosen by the user, then using set to update the options in the other menu.
function objpick
figure;
uicontrol('units','normalized','position',[0.1,0.2,0.3,0.05],...
'style','popup','string',{'Fruits','Vegetables','Marsupials'},...
'value',1,'callback',@changetype);
hm2 = uicontrol('units','normalized','position',[0.6,0.2,0.3,0.05],...
'style','popup','string',{''},'value',1);
function changetype(hObj,~)
switch get(hObj,'value')
case 1
s = {'Apple','Banana','Pear'};
case 2
s = {'Cabbage','Leek','Eggplant','Spinach'};
case 3
s = {'Wombat','Platypus','Kangaroo'};
end
set(hm2,'string',s,'callback',@dosomething)
end
end
