Is there material alteration when the serial number of a check had been altered?

No. An alteration is said to be material if it alters the effect of the instrument. It means an unauthorized change in an instrument that purports to modify in any respect the obligation of a party or an unauthorized addition of words or numbers or other change to an incomplete instrument relating to the obligation of a party. The alteration of the serial number of a check did not change the relations between the parties nor the effect of the instrument. Hence, the alteration on the serial number of a check is not a material alteration. (International Corporate Bank vs. CA, G.R. No. 141968, Feb. 12, 2001)