To combine like terms in the expression \( 9p^2q + 41pq^3 - 41pq^3 \), first, notice that the terms \( 41pq^3 \) and \(-41pq^3\) are like terms.
Now, when you combine those:
\[ 41pq^3 - 41pq^3 = 0 \]
So, the expression simplifies to:
\[ 9p^2q + 0 = 9p^2q \]
Thus, the final result after combining like terms is:
\[ \boxed{9p^2q} \]