Researchers in India discovered lycopene, which is found in watermelon, grapes, tomatoes and some sorts of shellfish, can boost sperm concentrations in infertile men.
There were even six pregnancies following the successful trial.
The researchers from the All India Institute of Medical Sciences in New Delhi, studied 30 infertile men.
The authors said: "We found that improvement in sperm concentration and motility was statistically significant.
"Oral lycopene therapy does seem to have a positive effect in the management of infertility of unknown causes."
Unexplained causes
The men, aged 23 to 45, took 2mg of oral lycopene twice each day for three months.
They found a direct correlation between lycopene levels and infertility.
Lycopene has already been linked with the treatment and prevention of oral cancer.
The researchers said: "Lycopene is one of the 650 carotenoids found in high concentration in male testes and lower levels of lycopene are found in infertile males."
The men studied had been infertile for between one and 20 years and its cause was unexplained.
Various deficiencies
The patients suffered from either a deficiency of sperm in semen, abnormal sperm structures, impaired sperm mobility and activity - some had all three sperm defects.
After taking lycopene for three months the doctors found that 67% of the patients had an improvement in the condition of their sperm.
Sperm mobility and activity were improved in 73% of patients and 63% showed an improvement in the sperm structure.
But the scientists said more work is needed before their research can be used in the fight against male infertility.
The researchers said: "Larger randomised controlled trials are essential before definitive therapeutic guidelines can be laid down."