This article describes how to highlight duplicate records arranged into a column each, if you are looking for records entered in a row each then go to this article: Highlight duplicate records. The image above shows one record in each column, cell range B2:E5.
The array formula and conditional formatting formula in this article contain the COUNTIFS function, a function introduced in excel 2007. The COUNTIFS function evaluates conditions on cells across multiple ranges and counts the number of times all are met.
Click "Use a formula to determine which cells to format"
Type =COUNTIFS($B$2:$E$2, B$2, $B$3:$E$3, B$3, $B$4:$E$4, B$4, $B$5:$E$5, B$5)>1 in "Format values where this formula is TRUE" window.
Click "Format.." button
Click "Fill" tab
Select a color for highlighting cells.
Explaining Conditional Formatting Formula in cell B2
Step 1 - Count columns that match the current column
In order to explain how this formula works you need to understand absolute and relative cell references. The dollar sign makes the cell reference locked, however a cell reference has both a column and row part and both may have a dollar sign depending on what you want to happen.
The COUNTIFS function allows you to counts duplicate records, make sure you create a condition for each row in your record. There are four rows in this example, the first argument is $B$2:$E$2 and doesn't change when the conditional formatting moves on to the next column.
The second argument is B$2 and is locked to row 2, however, the column is a relative cell reference (not locked) and changes when the CF moves to next column.
If there are columns that match all four conditions B$2, B$3, B$4 and B$5 then the COUNTIFS function returns the number of rows that match.