Hello AnandM, thank you for your help, but this is not what I'm looking for. I will try to explain better.
I need to pass to the page autocomplete.ashx a parameter in some way that does not involve the textbox which is autocompleted.
To be more specific I need to read the content of a label/parameter inside the page where the autocomplete textbox is located, and then pass it inside the page autocomplete.ashx, where I will read it with a request.querystring, or similar.
Then when I digit inside the autocomplete textbox I need that the query used filters with the parameter and with the things that I've digited inside the textbox. I hope that i was able to explain what I need.
Dim prefixText As String = context.Request.QueryString("q")
cmd.CommandText = ("select punto + '-' + ltrim(rtrim(coalesce(rag_soc,''))) + ' _ ' +coalesce(indirizzo,'') + ' ' + coalesce(citta,'') + ' - Tel.' + coalesce(cellulare,'') + ' - Card n.' + n_tessera as rag_soc from t_clienti where rag_soc like @SearchText + '%' and (punto='other parameter here') and cancellato='false' order by rag_soc")
cmd.Parameters.AddWithValue("@SearchText", prefixText)