The papers [Campi, Lecchini & Savaresi (2002). Autornatica, 38(8), 1337-1346; (2003). European Journal of Control, 9(l), 66-76] present a direct controller synthesis procedure that uses identification algorithms applied to filtered input-output plant data. This contribution discusses variations that, in some cases, may alleviate noise-induced correlation (in the open-loop case) and allow the applicability of the approach to unstable plants. Importantly, it also introduces an invalidation test step based on the available data (i.e., prior to experimental controller testing), to check if the flexibility of the controller parameterisation and the approximations involved are suitable for the design objectives or, on the contrary, the resulting closed loop may be unstable. (C) 2005 Elsevier Ltd. All rights reserved.