Your XML is invalid.. So I had to make a few assumptions.. Mainly that
the match is based on the elements name,, not the text() within the
element. I rattled it off quickly so I'm sure there is a nicer
solution out there.

<?xml version="1.0"?>
<record>
<product1>Item1</product1>
<product2>Item2</product2>
<product3>Item3</product3>
<serial1>serial 1</serial1>
<serial2>serial 2</serial2>
<serial3>serial 3</serial3>
</record>

<?xml version='1.0'?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="record">
	<xsl:apply-templates select="*[contains(name(), 'product')]"/>
</xsl:template>

<xsl:template match="*[contains(name(), 'product')]">
	<xsl:variable name="serialNum" select="concat('serial',
substring-after(., 'Item'))"/>
	<xsl:value-of select="."/><xsl:apply-templates
select="following-sibling::*[contains(name(), $serialNum)]"/>
</xsl:template>

<xsl:template match="*[contains(name(), 'serial')]">(<xsl:value-of
select="."/>)<xsl:text>
</xsl:text></xsl:template>

Item1(serial 1)
Item2(serial 2)
Item3(serial 3)

However, if the relationship is based on text() then you'll have to
replace name() with text() and 'product' with 'Item' and tweek at
match.

Hi All,
I have structure as
<record>
<product1>Item1</product1>
<product2>Item2</product2>
<product3>Item2</product2>
......
......
<serial1>serial 1</serial1>
<serial2>serial 2</serial2>
<serial3>serial 3</serial1>
.....
......

</record>
and I would get an an output as
Item1(serial 1)
Item2(serial 2)
Item3(serial 3)
...
I am not sure How I could do the substring and access the value of
other node and form the output as mentioned.

Please help me .