Evidence of five (5!!!) quark baryon found at the ELectron Stretcher Accelerator (ELSA) in Bonnn, Germany.
The SAPHIR collaboration announced evidence for Theta-plus with a mass of 1540 MeV and a width of less than 25 MeV, compatible with experimental results from SPring-8, ITEP and Jefferson Lab.
This exotic particle is allowed under the rules of Quantum Chromodynamics (QCD http://scienceworld.wolfram.com/physics/QuantumChromodynamics.html). It is composed of two up quarks, two down quarks and one anti-strange quark (uudd s-bar). It is called "exotic" because the antiquark is of a different flavor than the other quarks composing the baryon.
It's structure is interesting. It seems like it's got properties of both mesons and bayrons... I'll be reading this paper and posting a follow up.
More info here to be found:
[hep-ex/0307083] Evidence for the positive-strangeness pentaquark θ+ in photoproduction with the SAPHIR detector at ELSA