When neither the implementation nor the testing of an approach suggested by the prior art involves any particular technical difficulties, the consideration that the skilled person would have at least adopted a "try and see" attitude is a reason for denying inventive step (see e.g. T 333/97, T 377/95 of 24 April 2001 date: 2001-04-24, T 1045/98, T 1396/06, T 2168/11). In such situations the concept of "reasonable expectation of success" does not apply (T 91/98, T 293/07, T 259/15). The skilled person would prefer to verify whether the potential solution he had conceived worked, rather than abandon the project because success was not certain ("try and see" approach).

A "try and see" situation was considered to have occurred if the skilled person, in view of the teaching in the prior art, had already clearly envisaged a group of compounds or a compound and then determined by routine tests whether such compound/s had the desired effect (T 889/02, T 542/03, T 1241/03, T 1599/06, T 1364/08). See also in this chapter I.D.9.19.6 "Enhanced effect".

In T 1396/06 the board held that, in spite of the understandable uncertainties which always characterise biological experiments, the skilled person would have had no reason to adopt a sceptical attitude in the case in hand. He would have had either some expectations of success or, at worst, no particular expectations of any sort, but only a "try and see" attitude, which does not equate with an absence of a reasonable expectation of success (see also T 759/03).

In T 293/07 the board stated that the testing of humans could not be considered to represent known routine tests and accordingly the skilled person was not in a "try and see" situation. In T 847/07 the board considered it questionable whether the skilled person would adopt a "try and see" attitude at all in cases where extensive in vivo animal and ultimately human testing would be necessary in order to determine whether or not a compound has a certain property. See also T 1545/08.

In T 259/15 the board held that the case law did not support the conclusion that the skilled person would systematically avoid a "try-and-see" approach whenever testing on human patients was involved, regardless of the circumstances of the case. In the circumstances of the case in hand, the board considered that the skilled person would test the device in question (a buprenorphine transdermal patch) on human subjects despite the uncertainties as to the maximum duration of application.

In the light of the closest prior art the board saw the technical problem to be solved in T 886/91 in the exact identification and characterisation of DNA sequences of HVB genome subtype adyw. The board pointed out that the situation in T 886/91 could not be compared with the one in T 223/92 and T 500/91, where production of a partially known protein in a recombinant-DNA system was achieved and considered inventive on the basis of the fact that, in the specific circumstances of those cases, there was no realistic expectation of success. In the case in point the closest prior art had already disclosed the cloning and expression of the HBV genome subtype adyw. The identification and characterisation of the claimed specific sequences of the same genome involved for the skilled person nothing more than the performance of experimental work by routine means in connection with the normal practice of filling gaps in knowledge by the application of existing knowledge.

Decisions T 455/91 (OJ 1995, 684), T 412/93, T 915/93, T 63/94, T 856/94, T 91/98, T 111/00 and T 948/01 also consider this topic.