Closing database connections in 3 tier

[Edneeis]

I find it best to use a Try Catch block for data access and the close the connection in the Finally block. The Finally block executes at the end of normal execution or before exception moves on if there is an exception so it is a good fail safe way of making sure you clean up your connection.

Dim cnn As SQLConnection
Try
  cnn=New SQLConnection("myconnectionstring")
  cnn.Open()
  'my data operation
Catch ex As Exception
  'my exception handling
Finally
  If Not cnn Is Nothing AndAlso cnn.State=Open Then
     cnn.Close()
  End If
End Try

PS This is a good idea regardless of the Tiers you use or using the Application Blocks are good as well.