It seems as if Illumina (Nasdaq: ILMN) executives have been reading my article encouraging competitor Affymetrix (Nasdaq: AFFX) to expand further into diagnostic testing. Illumina announced on Friday that it's reorganized and created separate divisions for its life sciences and diagnostic businesses.

Illumina says the move was spurred by resignation and semiretirement of the current managers of its sequencing and arrays divisions, but one has to wonder whether the reorganization was the cause or effect of the personnel loss. In either case, I think it's a good move.

While Rule Breakers pick Affymetrix expands further into selling reagents to laboratories, competing against the likes of Invitrogen (Nasdaq: IVGN) and even giant Thermo Fisher Scientific (NYSE: TMO), Illumina seems to have figured out that the big-time growth is likely to be in diagnostics. You have to look no further than Ventana Medical Systems' (Nasdaq: VMSI) stock doubling in the last year or Bio-Rad Laboratories' (AMEX: BIO) bipolar growth to see that personalized medicine is spurring growth in the diagnostic field.

Affymetrix is still ahead of Illumina, since it has 10 partnerships set up for its CLIA-certified laboratory, but it looks like Illumina is clearly putting a greater emphasis on diagnostics. Hopefully it focuses on medical diagnostics and doesn't put too much emphasis on deCODE genetics' (Nasdaq: DCGN) and 23andMe's genome-wide tests, which I think will remain a niche product until the prices come down.

Illumina is presenting at the JPMorgan Healthcare Conference today, so investors may be able to get a better view of its plans by watching the webcast. If you hear them give me credit, be sure to shoot me an email.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.