A process for detecting HIV infection, Hepatitis A, B and C, and other similar infections in a plasma sample, wherein the process involves the use of an excitation laser source to irradiate upon the plasma sample an excitation laser beam to obtain a fluorescence emission spectrum of the plasma sample. The invention uses an excitation laser wavelength of about 355 nanometers. Detection of the fluorescence is made in the wavelength range from about 380 to 600 nanometers. The resulting spectrum of the sample is compared with the spectrum of a control which is free from infection. Analysis of the parameters of the emission spectra including, but not limited to, peak intensity wavelength, amplitude at the peak intensity, area ratio of left and right portions of the emission spectra, and shifts of the peak intensity wavelength, allows determination of HIV infection, Hepatitis A, B and C, and other similar infection in the plasma. Selective absorbents, such as C-M Affi Gel Blue and activated charcoal, may be used to treat the samples before fluorescence measurements, which is found to improve discrimination of infected and uninfected samples. The present invention is capable of detecting HIV infection at the stage when it is still undetectable by conventional diagnosis methods.