Excel VBA Problem!

Hi Highly Esteemed Experts,

I have two Excel columns - A and B - and I am trying to write VBA code that will search each used field of two columns for certain keywords in this manner:
1.) If keyword is present in the first column, then populate cell D1 (for example) with a defined text.

2.) If keyword is not present in the first column A, search column B of the same record for the keywords.

I am using instr() for the search, I can successfully search the first column - does any one know how I can use instr() with select case in defining what to put in D1? to avoid lengthy and awkward if then else statements.

I am putting all these in a Do Until....Loop function.